View source for Assured clear distance ahead

{{Short description|Safe driving distance between cars}}
{{use mdy dates|date=September 2021}}
{{Use American English|date = April 2019}}
{{Self-driving car}}
In legal terminology, the '''assured clear distance ahead''' ('''ACDA''') is the distance ahead of any terrestrial [[travel|locomotive]] device such as a [[land vehicle]], typically an [[automobile]], or [[watercraft]], within which they should be able to bring the device to a halt.<ref name="CDLM"/> It is one of the most fundamental principles governing [[ordinary care]] and the [[duty of care]] for all methods of conveyance, and is frequently used to determine if a driver is in proper control and is a nearly universally implicit consideration in vehicular accident liability.<ref name="NY Jur">{{cite book |title=New York Jurisprudence |series=Automobiles and Other Vehicles |number=4A |page=§ 720 |author=Lawyers Cooperative Publishing |location=Miamisburg, OH |publisher=LEXIS Publishing |url=https://legalsolutions.thomsonreuters.com/law-products/Legal-Encyclopedias/New-York-Jurisprudence-2d/p/100029357 |oclc=321177421 |quote=It is negligence as a matter of law to drive a motor vehicle at such a rate of speed that it cannot be stopped in time to avoid an obstruction discernible within the driver's length of vision ahead of him. This rule is known generally as the 'assured clear distance ahead' rule * * * In application, the rule constantly changes as the motorist proceeds, and is measured at any moment by the distance between the motorist's vehicle and the limit of his vision ahead, or by the distance between the vehicle and any intermediate discernible static or forward-moving object in the street or highway ahead constituting an obstruction in his path. Such rule requires a motorist in the exercise of due care at all times to see, or to know from having seen, that the road is clear or apparently clear and safe for travel, a sufficient distance ahead to make it apparently safe to advance at the speed employed.}}</ref><ref name="Leibowitz&Herschel">{{cite journal |last1=Leibowitz |first1=Herschel W. |last2=Owens |first2=D. Alfred |last3=Tyrrell |first3= Richard A. |year=1998 |title=The assured clear distance ahead rule: implications for nighttime traffic safety and the law |journal=Accident Analysis & Prevention |volume=30 |issue=1 |pages=93–99 |doi=10.1016/S0001-4575(97)00067-5 |pmid=9542549 |quote=The assured clear distance ahead (ACDA) rule holds the operator of a motor vehicle responsible to avoid collision with any obstacle that might appear in the vehicle's path.}}</ref><ref name="75 ALR.3d 327">{{cite book |title=American Law Reports--Annotated, 3rd Series |chapter=Automobiles: sudden emergency as exception to rule requiring motorist to maintain ability to stop within assured clear distance ahead |author=James O. Pearson |publisher=The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company |volume=75 |page=327 |year=2009}}</ref> The rule is a precautionary trivial burden required to avert the great probable gravity of precious life loss and momentous damage.<ref name="Newton"/><ref name="Kloeden et. al."/><ref name="material cost of accidents">{{cite news |title=Insurers Brace for a Self-Driving Future (and a Fading Need for Insurance). |author=Benjamin Preston |date=January 8, 2016 |newspaper=[[The New York Times]] |page=B3 |url=https://www.nytimes.com/2016/01/08/automobiles/insurers-brace-for-the-self-driving-future-and-fewer-accidents.html}}</ref> Satisfying the ACDA rule is necessary but not sufficient to comply with the more generalized [[Assured clear distance ahead#ACDA rule-specific case generalized to the Basic Speed Law|basic speed law]], and accordingly, it may be used as both a layman's criterion and judicial [[Test (law)|test]] for courts to use in determining if a particular speed is negligent, but not to prove it is safe.<ref>{{cite journal |author=Murray Carl Lertzman |title=The Assured Clear Distance Ahead Rule in Ohio |journal=Case Western Reserve Law Review |volume=5 |number=1 |pages=77–83 |date=1954 |url=https://scholarlycommons.law.case.edu/caselrev/vol5/iss1/7 |quote=when an automobile collides with an obstruction on the highway it becomes important to determine whether the driver was exceeding a speed which would have permitted him to stop within his assured clear distance ahead...whenever a driver has collided with a readily discernible object located ahead of him and within his lane of travel for a substantial period of time, he has been held, as a matter of law, to have been negligent. Under such circumstances, the courts have indicated that the fact that a collision occurred furnishes evidence from which reasonable minds could only conclude that the driver was traveling at such a speed that he was unable to stop within the assured clear distance ahead}}</ref> As a spatial [[standard of care]], it also serves as required explicit and fair notice of prohibited conduct so unsafe speed laws are not [[void for vagueness]].<ref name="269 US 385"/><ref name="1998 MT 321"/><ref name="void for vagueness"/> The concept has transcended into [[Traffic collision reconstruction|accident reconstruction]] and engineering.<ref name=":0"/>

This distance is typically both determined and constrained by the proximate edge of clear visibility, but it may be attenuated to a margin of which beyond hazards may reasonably be expected to spontaneously appear. The rule is the specific spatial case of the common law [[Speed limit#Reasonable speed|basic speed rule]],<ref name="189 Cal. 335"/> and an application of ''[[volenti non fit injuria]]''. The [[two-second rule]] may be the limiting factor governing the ACDA, when the speed of forward traffic is what limits the basic safe speed, and a primary hazard of collision could result from following any closer.<ref name="NY Jur"/><ref name="Leibowitz&Herschel"/>

As the original [[common law]] driving rule preceding statutized [[traffic law]],<ref name="189 Cal. 335"/> it is an ever important foundational rule in today's complex driving environment. Because there are now protected classes of roadway users—such as a [[school bus]], [[mail carrier]], [[emergency vehicle]], [[horse-drawn vehicle]], [[agricultural machinery]], [[street sweeper]], [[disabled vehicle]],<ref name="235 N.C. 568"/> [[cyclist]], and [[pedestrian]]—as well as [[natural hazards]] which may occupy or obstruct the roadway beyond the edge of visibility,<ref name="235 N.C. 568"/> negligence may not depend ''[[ex post facto]]'' on what a driver happened to hit, could not have known, but had a concurrent duty to avoid.<ref name="189 Cal. 335"/><ref name="100 Cal. App. 2d 411"/> Furthermore, modern knowledge of [[human factors]] has revealed physiological limitations—such as the [[Visual acuity#Subtended angular velocity detection threshold (SAVT)|subtended angular velocity detection threshold]] (SAVT)—which may make it difficult, and in some circumstance impossible, for other drivers to always comply with [[Right-of-way (traffic)|right-of-way]] statutes by staying clear of roadway.<ref name="Hoffmann & Mortimer"/><ref name="Maddox"/>
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==As common law rule or statute==
===Origins===
As with the genesis of most legal doctrine governing problems which precede a legislative solution, the ACDA principle generally originates to decisional [[precedent]] by high courts which [[logical reasoning|reasoned]] general common sense rules of conduct of which naturally follow from the repetitive process of determining specific culpability.<ref name="common law2">{{cite court |litigants=The Batavier |vol=40 |reporter=English Reports in Law and Equity |opinion=19–27 |pinpoint=25 |court=Great Britain. Courts.; Great Britain. Parliament. House of Lords.; Great Britain. Privy Council. Judicial Committee |date=July 14, 1854 |url=http://babel.hathitrust.org/cgi/pt?id=osu.32437121385286;view=1up;seq=35 |publisher=Boston, C.C. Little and J. Brown |oclc=4370213 |quote=Page 25: At whatever rate she (the steamer) was going, if going at such a rate as made it dangerous to any craft which she ought to have seen, and might have seen, she had no right to go at that rate. ... at all events, she was bound to stop if it was necessary to do so, in order to prevent damage being done ... [http://catalog.hathitrust.org/Record/100187260 See more English Reports in Law and Equity]}}</ref><ref name="Newton">{{cite court |litigants=Newton v. Stebbins, 51 U.S. 586 |vol=51 |reporter=[[United States Reports]] |opinion=586 |court=[[Supreme Court of the United States]] |date=December 1850 |url=https://www.law.cornell.edu/supremecourt/text/51/586 |quote=it may be a matter of convenience that steam vessels should proceed with great rapidity, but the law will not justify them in proceeding with such rapidity if the property and lives of other persons are thereby endangered. ... It is a mistake to suppose that a rigorous enforcement of the necessity of adopting precautionary measures by the persons in charge of steamboats to avoid damage to sailing vessels on our rivers and internal waters will have the effect to produce carelessness and neglect on the part of the persons in charge of the latter. The vast speed and power of the former, and consequent serious damage to the latter in case of a collision, will always be found a sufficient admonition to care and vigilance on their part. A collision usually results in the destruction of the sailing vessel, and not infrequently in the loss of the lives of persons on board.}}</ref><ref name="common law">{{cite court |litigants=The Europa |vol=2 |reporter=English Reports in Law and Equity |opinion=557–564 |pinpoint=564 |court=Great Britain. Courts.; Great Britain. Parliament. House of Lords.; Great Britain. Privy Council. Judicial Committee |date=June 11, 1850 |url=http://babel.hathitrust.org/cgi/pt?id=osu.32437121385120;view=1up;seq=575 |publisher=Boston, C.C. Little and J. Brown |oclc=4370213 |quote=Page: 564 Whether any given rate is dangerous or not must depend upon the circumstances of each individual case, as the state of the weather, locality, and other similar facts. [http://catalog.hathitrust.org/Record/100187260 See more English Reports in Law and Equity]}}</ref><ref name="The Colorado">{{cite court |litigants=The Colorado, 91 U.S. 692 |vol=91 |reporter=[[United States Reports]] |opinion=692 |court=[[Supreme Court of the United States]] |date=October 1875 |url=https://supreme.justia.com/cases/federal/us/91/692/case.html |quote=when steamships are approaching another ship so as to involve risk of collision, they shall slacken their speed or, if necessary, stop and reverse, and the express provision is that every steamship shall, when in a fog, go at a moderate speed.}}</ref><ref name="141 Wis. 57"/><ref name="360 S.W.2d 64"/> Legislation often subsequently followed which either superfluously codified and endorsed or revised these principles,<ref name="IMO">{{cite web |url=http://www.dft.gov.uk/mca/msn_1781-2.pdf |archive-url=http://webarchive.nationalarchives.gov.uk/20121107103953/http://www.dft.gov.uk/mca/msn_1781-2.pdf |archive-date=November 7, 2012 |title=International Regulations for Preventing Collisions at Sea |publisher=International Maritime Organization (IMO), United Nations |date=October 20, 1972 |at=Part B, Section I, Rule 6}}</ref><ref name="RS 4233">{{cite web |url=http://uscode.house.gov/statviewer.htm?volume=rs&page=815 |title=Revised Statutes (1878), Title XLVIII (48), Chapter 5: Navigation, Section 4233, rules for preventing collisions |publisher=[[Congress of the United States]] |date=1878 |quote=Rule twenty-one. Every steam-vessel, when approaching another vessel, so as to involve risk of collision, shall slacken her speed, or, if necessary, stop and reverse: and every steam-vessel shall, when in a fog, go at a moderate speed}}</ref> of which courts would in turn continue to flesh out the details.<ref name="Nacoochee">{{cite court |litigants=The Nacoochee v. Moseley, 137 U.S. 330 |vol=137 |reporter=[[United States Reports]] |opinion=330 |court=[[Supreme Court of the United States]] |date=December 8, 1890 |url=https://www.law.cornell.edu/supremecourt/text/137/330 |quote=every steam-vessel, when approaching another vessel, so as to involve risk of collision, shall slacken her speed, or, if necessary, stop and reverse; and every steam-vessel shall, when in a fog, go at a moderate speed. ... She was bound, therefore, to observe unusual caution, and to maintain only such a rate of speed as would enable her to come to a standstill, by reversing her engines at full speed, before she should collide with a vessel which she should see through the fog. ... whatever rate a steamer was going, if she was going at such a rate as made it dangerous to any craft which she ought to have seen, and might have seen, she had no right to go at that rate.}}</ref><ref name="42 Ohio App. 520"/><ref name="216 Iowa 170"/> By the late 1920s, the term ''"assured clear distance ahead"'' came into widespread use as the identity of a standard of care element in choosing safe speed,<ref>{{cite web |title=Ohio General Code, Section 12603 |url=https://casetext.com/case/curtis-v-hubbel |date=July 21, 1929 |quote=Section 12603, General Code, which was amended at the legislative session of 1929 (113 Ohio Laws, 283), becoming effective July 21, 1929, wherein, for the first time, appears the following: "No person shall drive any motor vehicle in and upon any public road or highway at a greater speed than will permit him to bring it to a stop within the assured clear distance ahead."}}</ref><ref>{{cite web |title=Iowa General Code, Section 5029 (1931) |url=https://casetext.com/case/lindquist-v-thierman |date=1931 |quote=I.G.C., § 5029 (1931): any person driving a motor vehicle on a highway shall drive the same at a careful and prudent speed not greater than nor less than is reasonable and proper, having due regard to the traffic, surface and width of the highway, * * * and no person shall drive any vehicle upon a highway at a speed greater than will permit him to bring it to a stop within the assured clear distance ahead.}}</ref> with differing jurisdictions adopting the language to carry its same effects.<ref>{{cite court |litigants=McCool v. Smith |vol=66 |reporter=United States Reports |opinion=459 |pinpoint=469 |court=[[Supreme Court of the United States]] |date=1861 |url=https://supreme.justia.com/cases/federal/us/66/459/case.html |quote=It is a sound rule, that whenever our Legislature use a term without defining it, which is well known in the [[Common law|English law]], and there has been a definite appropriate meaning affixed to it, they must be supposed to use it in the sense in which it is understood in the [[Common law|English law]].'}}</ref><ref>{{cite court |litigants=Shapiro v. United States |vol=335 |reporter=United States Reports |opinion=1 |pinpoint=16 |court=[[Supreme Court of the United States]] |date=1941 |url=https://supreme.justia.com/cases/federal/us/335/1/case.html |quote=In adopting the language used in the earlier act, Congress "must be considered to have adopted also the construction given by this Court to such language, and made it a part of the enactment."}}</ref> Much of the earliest published record naturally pertains to high stakes wrecks<ref name="common law2"/><ref name="141 Wis. 57"/> among vessels<ref>{{cite web |url=http://uscode.house.gov/statviewer.htm?volume=rs&page=1 |title=Revised Statutes (1878), Title I General Provisions, Chapter 1, Section 3: Vessel |publisher=[[Congress of the United States]] |date=1878 |quote=The word "vessel" includes every description of water-craft or other artificial contrivance used, or capable of being used, as a means of transportation on water.}}</ref> or vehicles<ref name="Revised Statutes 4233">{{cite web |url=http://uscode.house.gov/statviewer.htm?volume=rs&page=2 |title=Revised Statutes (1878), Title I General Provisions, Chapter 1, Section 4: Vehicle |publisher=[[Congress of the United States]] |date=1878 |quote=The word "vehicle" includes every description of carriage or other artificial contrivance used, or capable of being used, as a means of transportation on land.}}</ref> as defined in those times, though the obvious principle applies to [[chariots]] and might in fact be [[time immemorial]].<ref name="189 Cal. 335"/><ref name="Nixon"/><ref name="175 Cal. 497"/>

===Present===
Horses may still be expected to use the roadways, as well bicycles and automobiles.<ref name="CVC 21050">{{cite web |title=California Vehicle Code §21050 |publisher=State of California |url=http://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=VEH&sectionNum=21050. |quote=every person riding or driving an animal upon a highway has all of the rights and is subject to all of the duties applicable to the driver of a vehicle}}</ref><ref name="CVC 21759">{{cite web |title=California Vehicle Code §21759 |publisher=State of California |url=http://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=VEH&sectionNum=21759. |quote=The driver of any vehicle approaching any horse drawn vehicle, any ridden animal, or any livestock shall exercise proper control of his vehicle and shall reduce speed or stop as may appear necessary or as may be signalled or otherwise requested by any person driving, riding or in charge of the animal or livestock in order to avoid frightening and to safeguard the animal or livestock and to insure the safety of any person driving or riding the animal or in charge of the livestock.}}</ref><ref name="CVC 21200">{{cite web |title=California Vehicle Code §21200 |publisher=State of California |url=http://leginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=VEH&sectionNum=21200 |quote=A person riding a bicycle or operating a pedicab upon a highway has all the rights and is subject to all the provisions applicable to the driver of a vehicle by this division, including, but not limited to, provisions concerning driving under the influence of alcoholic beverages or drugs}}</ref> The former are a regular appearance in both [[urban areas]] and in the [[Rural area|country]], and are commonly exercised by [[Bicycle commuting|commuters]] and [[Amish]]. Many roads are unchanged since the 1800s while [[controlled-access highways]] have been invented specifically for the automobile.<ref>[[Leyden Street]] remains unchanged since 1620</ref> "At [[common law]] a motorist is required to regulate his speed so that he can stop within the range of his vision. In numerous jurisdictions, this rule has been incorporated in [[statutes]] which typically require that no person shall drive any motor vehicle in and upon any public road or highway at a greater speed than will permit him to bring it to a stop within the assured clear distance ahead."<ref name="75 ALR.3d 327"/><ref name="189 Cal. 335"/> [[Case law|Decisional law]] usually settles the circumstances by which a portion of the roadway is assuredly clear without it being mentioned in statute.<ref name="NY Jur"/> States where the judiciary has explicitly established the state's ACDA law include Indiana,<ref>{{cite court |litigants=Pennsylvania R. Co. v. Huss, 96 Ind. App. 71, 180 N. E. 919 |vol=96 |reporter=Indiana Appellate Reports |opinion=71 |court=[[Court of Appeals of Indiana]] |date=May 6, 1932 |url=https://casetext.com/case/pennsylvania-railroad-co-v-huss |quote=it is a violation of the law, and, therefore negligence, to drive an automobile at such speed, in the daytime or night time, that it cannot be stopped within the distance that objects can be seen ahead if proper lights are used}}</ref> Iowa,<ref name="216 Iowa 170">{{cite court |litigants=Lindquist v. Thierman, 216 Iowa 170 |vol=216 |reporter=Iowa |opinion=170 |court=[[Iowa Supreme Court]] |date=May 15, 1933 |url=https://casetext.com/case/lindquist-v-thierman |quote=it is evident that the words "within the assured clear distance ahead", as used in the statute, signify that the operator of the automobile, when driving at night as well as in the day, shall at all times be able to stop his car within the distance that discernible objects may be seen ahead of it.}}</ref> Kansas,<ref>{{cite court |litigants=Fisher v. O'Brien, 99 Kan. 621, 192 Pac. 317, L.R.A. 1917F, 610 |date=1917}}</ref> Louisiana,<ref>{{cite court |litigants=Demerest v. Travelers Insurance Company, 234 La. 1048 |vol=234 |reporter=La. |opinion=1040 |court=[[Supreme Court of Louisiana]] |date=April 21, 1958 |url=http://law.justia.com/cases/louisiana/supreme-court/1958/234-la-1048-0.html |quote=the jurisprudence of this state is that: "when visibility is materially impaired because of smoke, mist, dust, etc., a motorist should reduce his rate of speed to such extent and keep his car under such control as to reduce to a minimum the possibility of accident from collision; and as an extreme measure of safety, it is his duty, when visibility ahead is not possible or greatly obscured, to stop his car and remain at a standstill until conditions warrant going forward.}}</ref><ref>{{cite court |litigants=Carriere v. Aetna Cas. Co., 146 So.2d 451 |vol=146 |reporter=So.2d |opinion=451 |court=Court of Appeal of Louisiana. Fourth Circuit |date=October 1, 1962 |url=https://casetext.com/case/carriere-v-aetna-casualty-company |quote=The law is settled to the effect that a motorist is held to have seen an object which, by the use of ordinary care and prudence, he should have seen in time to avoid running into it, and that the driver of an automobile is guilty of negligence in driving at a rate of speed greater than that in which he could stop within the range of his vision.}}</ref> Michigan,<ref>{{cite court |litigants=Spencer v. Taylor, 219 Mich. 110, 188 N.W. 461 (1922) |vol=219 |reporter=Mich. |opinion=110 |date=1922}}</ref><ref>{{cite court |litigants=Gleason v. Lowe, 232 Mich. 300 |vol=232 |reporter=Mich. |opinion=300 |court=[[Supreme Court of Michigan]] |date=October 1, 1925 |url=https://casetext.com/case/gleason-v-lowe |quote=...every man must operate his automobile so that he can stop it within the range of his vision, whether it be daylight or darkness. It makes no difference what may obscure his vision, whether it be a brick wall or the darkness of nightfall. ... He must ... be able to see where he is going, and if his range of vision is 50 feet, if he can see 50 feet ahead of him, he must regulate his speed so that he can stop in a distance of 50 feet; if he can see 20 feet ahead of him, he must regulate his speed so that he can stop within 20 feet, and so on.}}</ref><ref name="245 Mich. 88">{{cite court |litigants=Ruth v. Vroom, 245 Mich. 88, 222 N. W. 155, 62 A. L. R. 1528 |vol=245 |reporter=Mich. |opinion=88 |court=[[Supreme Court of Michigan]] |date=December 4, 1928 |url=https://casetext.com/case/ruth-v-vroom |quote=It is settled in this State that it is negligence as a matter of law to drive an automobile at night at such speed that it cannot be stopped within the distance that objects can be seen ahead of it; and, if a driver's vision is obscured by the lights of an approaching car, it is his duty to slacken speed and have his car under such control that he can stop immediately if necessary. ... The rule adopted by this court does not raise merely a rebuttable presumption of negligence. It is a rule of safety. ... It is not enough that a driver be able to begin to stop within the range of his vision, or that he use diligence to stop after discerning an object. The rule makes no allowance for delay in action.}}</ref> New York,<ref name="74 A.D.2d 806">{{cite court |litigants=O'Farrell v. Inzeo, 74 A.D.2d 806 (1st Dept. 1980) |vol=74 |reporter=A.D.2d |opinion=806 |court=[[New York Supreme Court, Appellate Division]] |date=1980 |url=https://scholar.google.com/scholar_case?case=9540633306602447263 |quote=It is negligence as a matter of law to drive a motor vehicle at such a rate of speed that it cannot be stopped in time to avoid an obstruction discernible within the driver's length of vision ahead of him. This rule is known generally as the 'assured clear distance ahead' rule * * * In application, the rule constantly changes as the motorist proceeds, and is measured at any moment by the distance between the motorist's vehicle and the limit of his vision ahead, or by the distance between the vehicle and any intermediate discernible static or forward-moving object in the street or highway ahead constituting an obstruction in his path. Such rule requires a motorist in the exercise of due care at all times to see, or to know from having seen, that the road is clear or apparently clear and safe for travel, a sufficient distance ahead to make it apparently safe to advance at the speed employed.}}</ref> North Carolina,<ref name="235 N.C. 568">{{cite court |litigants=Morris v. Jenrette Transport Co. |vol=235 |reporter=N.C. |opinion=568 |court=[[Supreme Court of North Carolina]] |date=May 21, 1952 |url=http://law.justia.com/cases/north-carolina/supreme-court/1952/451-2-1.html |access-date=February 2016 |quote=It is not enough that the driver of plaintiff's automobile be able to begin to stop within the range of his lights, or that he exercise due diligence after seeing defendants' truck on the highway. He should have so driven that he could and would discover it, perform the manual acts necessary to stop, and bring the automobile to a complete stop within the range of his lights. When blinded by the lights of the oncoming car so that he could not see the required distance ahead, it was the duty of the driver within such distance from the point of blinding to bring his automobile to such control that he could stop immediately, and if he could not then see, he should have stopped. In failing to so drive he was guilty of negligence which patently caused or contributed to the collision with defendants' truck, resulting in injury to plaintiff."...it was his duty to anticipate presence of others, [...] and hazards of the road, such as disabled vehicle, and, in the exercise of due care, to keep his automobile under such control as to be able to stop within the range of his lights}}</ref> Ohio,<ref name="42 Ohio App. 520">{{cite court |litigants=Curtis v. Hubbel, 42 Ohio App. 520, 182 N. E. 589 |vol=42 |reporter=Ohio App. |opinion=520 |court=[[Ohio District Courts of Appeals|Court of Appeals of Ohio]] |date=May 31, 1932 |url=https://casetext.com/case/curtis-v-hubbel |quote=Statute requiring drivers to maintain speed permitting them to stop within assured clear distance ahead held applicable to both day and night driving ... Motorist unable, because of insufficient headlights, to see pedestrian until within few feet, must be able to stop within such distance, and failure to drive at speed permitting such stopping is negligence ''per se''.}}</ref><ref name="49 Ohio St.2d 5">{{cite court |litigants=Blair v. Goff-Kirby Co. |vol=49 |reporter=Ohio St.2d |opinion=5 |pinpoint=7 |court=[[Supreme Court of Ohio]] |date=December 29, 1976 |url=http://www.leagle.com/decision/19765449OhioSt2d5_153/BLAIR%20v.%20GOFF-KIRBY%20CO. |access-date=February 2016 }}</ref> Tennessee,<ref name="360 S.W.2d 64">{{cite court |litigants=Garner v. Maxwell, 360 S.W.2d 64 |vol=360 |reporter=S.W.2d |opinion=64 |court=[[Tennessee Court of Appeals|Court of Appeals of Tennessee]] |date=December 20, 1961 |url=http://www.ecases.us/case/tennctapp/c3628031/garner-v-maxwell |quote=What is known as the {{sic|hide=y|reason=double 'the' error in source}} "The assured clear distance rule" arises out of the decision of the Supreme Court in 1914 in the case of West Construction Co. v. White, 130 Tenn. 520, 172 S.W. 301, in which case it was held that the failure of a plaintiff to stop his car within the distance lighted by the headlights of the car, and thus avoid a collision, amounted, as a matter of law, to contributory negligence which barred plaintiff's suit.}}</ref><ref name="130 Tenn. 520">{{cite court |litigants=West Constr. Co. v. White, 130 Tenn. 520, 172 S.W. 301 |date=1914 |quote=It was negligence for the driver of the automobile to propel it in a dark place in which he had to rely on the lights of his machine at a rate faster than enabled him to stop or avoid any obstruction within the radius of his light, or within the distance to which his lights would disclose the existence of obstructions ...If the lights on the automobile would disclose obstructions only ten yards away, it was the duty of the driver to regulate his speed of his machine that he could at all times avoid obstructions within that distance.}}</ref> Vermont,<ref>{{cite court |litigants=Steele v. Fuller, 104 Vt. 303 |vol=104 |reporter=Vt. |opinion=303 |publisher=[[Supreme Court of Vermont]] |date=November 1932 |url=https://casetext.com/case/steele-v-fuller |quote=Operator of motor vehicle has duty at all times to maintain lookout for persons and property on highway, and to use reasonable care to avoid inflicting injuries on such persons or property. ... Operator of motor vehicle is chargeable with knowledge of objects in highway which are in plain view. ... One who drives automobile along public highway in dark must drive at such speed that automobile can be stopped within range of its headlights. ... Rule that automobile operator may assume that other motorists would not obstruct highway unlawfully, and would show statutory lights if they stopped, applies only in favor of one whose own conduct measures up to that of prudent and careful man in like circumstances.}}</ref> Wisconsin,<ref name="141 Wis. 57">{{cite court |litigants=Lauson v. Town of Fond du Lac, 141 Wis. 57, 123 N. W. 629, 25 L. R. A. (N. S.) 40. |vol=141 |reporter=Wis. |opinion=57 |court=[[Wisconsin Supreme Court]] |date=1909 |quote=the driver of an automobile, circumstanced as was the driver of the car in which the plaintiff was riding, and operating it under such conditions as he operated his machine on the night of the accident, is not exercising ordinary care if he is driving the car at such a rate of speed that he cannot bring it to a standstill within the distance that he can plainly see objects or obstructions ahead of him}}</ref><ref name="217 Wis. 465">{{cite court |litigants=Mann v. Reliable Transit Co., 217 Wis. 465, 259 N. W. 415 |vol=217 |reporter=Wis. |opinion=465 |court=[[Wisconsin Supreme Court]] |date=1935}}</ref> and California.<ref>{{cite court
|litigants=Satterlee v. Orange Glenn School Dist., 29 Cal.2d 581
|vol=29
|reporter=Official California Reports, 2nd Series
|opinion=581
|court=[[California Supreme Court]]
|date=Jan 31, 1947
|url=http://scocal.stanford.edu/opinion/satterlee-v-orange-glenn-school-dist-25951
|access-date=2013-09-01
|quote="proper conduct of a reasonable person under particular situations may become settled by judicial decision or be prescribed by statute or ordinance."
}} See [http://www.lexisnexis.com/clients/CACourts/ California Official Reports: Online Opinions]
</ref><ref name="156 Cal.App.2d 374">{{cite court
|litigants=Wilding v. Norton, 156 Cal.App.2d 374
|vol=156
|reporter=Official California Appellate Reports, 2nd Series
|opinion=374
|court=[[California courts of appeal|California Appellate Court]]
|date=December 27, 1957
|publisher=Bancroft-Whitney; LexisNexis 
|url=http://law.justia.com/cases/california/court-of-appeal/2d/156/374.html
|quote=The so-called basic speed law is primarily a regulation of the conduct of the operators of vehicles. They are bound to know the conditions which dictate the speeds at which they can drive with a reasonable degree of safety. '''They know, or should know,''' their cars and their own ability to handle them, and '''especially their ability to come to a stop at different speeds and under different conditions of the surface of the highway'''. [http://www.lexisnexis.com/clients/CACourts/ See Official Reports Online]}}</ref><ref name="100 Cal. App. 2d 411"/><ref name="179 Cal. 349"/><ref name="175 Cal. App. 2d 140">{{cite court
|litigants=Lutz v. Schendel, 175 Cal. App. 2d 140
|vol=175
|reporter=Official California Appellate Reports, 2nd Series
|opinion=140
|court=[[California courts of appeal|California Appellate Court]] 
|date=Nov 6, 1959
|publisher=Bancroft-Whitney; LexisNexis
|url=http://law.justia.com/cases/california/calapp2d/175/140.html
|access-date=2013-09-01
|quote="It is the '''duty''' of the driver of a motor vehicle using the public highways to be vigilant at all times and to keep the vehicle under such control that to avoid a collision he can '''stop as quickly as might be required''' of him by eventualities that would be anticipated by an ordinarily prudent driver in like position."}} See [http://www.lexisnexis.com/clients/CACourts/ California Official Reports: Online Opinions]</ref>

Many states have further passed [[statutes]] which require their courts to more inflexibly weigh the ACDA in their determination of reasonable speed or behavior. Such statutes do so in part by designating ACDA violations as a citable driving offense, thus burdening an offending driver to rebut a [[Negligence per se|presumption of negligence]]. States with such explicit ACDA [[standard of care]] provisions include: Iowa,<ref>{{cite web |url=https://www.legis.iowa.gov/DOCS/IACODE/2001/321/285.html |title=Code § 321.285 Speed restrictions. |publisher=The State of Iowa |access-date=August 6, 2013 |quote=Any person driving a motor vehicle on a highway shall drive the same at a careful and prudent speed not greater than nor less than is reasonable and proper, having due regard to the traffic, surface, and width of the highway and of any other conditions then existing, and no person shall drive any vehicle upon a highway at a speed greater than will permit the person to bring it '''to a stop within the assured clear distance ahead''', such driver having the right to assume, however, that all persons using said highway will observe the law.}}</ref> Michigan,<ref>{{cite web |url=http://www.legislature.mi.gov/(S(rgjlv4453ryguemx2ko5fpzi))/printDocument.aspx?objectName=mcl-257-627&version=txt |title=§ 257.627 Speed limitations |publisher=The State of Michigan |access-date=August 6, 2013 |quote=§ 257.627(1) A person operating a vehicle on a highway shall operate that vehicle at a careful and prudent speed not greater than nor less than is reasonable and proper, having due regard to the traffic, surface, and width of the highway and of any other condition then existing. '''A person shall not operate a vehicle upon a highway at a speed greater than that which will permit a stop within the assured, clear distance ahead'''.}}</ref> Ohio,<ref>{{cite web |url=http://codes.ohio.gov/orc/4511.21v1 |title=Revised Code § 4511.21(A) Speed limits - assured clear distance |publisher=The State of Ohio |access-date=August 6, 2013 |quote=§ 4511.21(A)(A) No person shall operate a motor vehicle, trackless trolley, or streetcar at a speed greater or less than is reasonable or proper, having due regard to the traffic, surface, and width of the street or highway and any other conditions, and no person shall drive any motor vehicle, trackless trolley, or streetcar in and upon any street or highway at a greater speed than will permit the person to bring it '''to a stop within the assured clear distance ahead'''.}}</ref> Oklahoma,<ref>{{cite web |url=http://oklegal.onenet.net/oklegal-cgi/get_statute?98/Title.47/47-11-801.html |title=Oklahoma Statutes § 47-11-801 |publisher=The State of Oklahoma |access-date=August 6, 2013 |quote=A. Any person driving a vehicle on a highway shall drive the same at a careful and prudent speed not greater than nor less than is reasonable and proper, having due regard to the traffic, surface and width of the highway and any other conditions then existing, and '''no person shall drive any vehicle upon a highway at a speed greater than will permit the driver to bring it to a stop within the assured clear distance ahead'''.}}</ref> Pennsylvania,<ref>{{cite web |url=http://www.legis.state.pa.us/WU01/LI/LI/CT/HTM/75/00.033.061.000..HTM |title=75 Pa. Cons. Stat. § 3361. Driving vehicle at safe speed |publisher=The State of Pennsylvania |access-date=August 6, 2013 |quote=No person shall drive a vehicle at a speed greater than is reasonable and prudent under the conditions and having regard to the actual and potential hazards then existing, '''nor at a speed greater than will permit the driver to bring his vehicle to a stop within the assured clear distance ahead'''.}}</ref> and Texas.<ref>{{cite web |title=Transportation Code, Title 7, Ch. 545, §545.062(a) |publisher=State of Texas |access-date=25 March 2018 |url= http://www.statutes.legis.state.tx.us/Docs/TN/htm/TN.545.htm |quote=An operator shall, if following another vehicle, maintain an '''assured clear distance''' between the two vehicles so that, considering the speed of the vehicles, traffic, and the conditions of the highway, the operator can safely stop without colliding with the preceding vehicle or veering into another vehicle, object, or person on or near the highway.}}</ref>

States which apply the principle by statute to watercraft on navigable waterways include all 174 member states of the [[International Maritime Organization]],<ref>{{cite web |url=http://www.imo.org/en/About/Membership/Pages/MemberStates.aspx |title=Member States |publisher=International Maritime Organization (IMO), United Nations |access-date=3 July 2018 |quote=Members of IMO are governed by [[International Regulations for Preventing Collisions at Sea#Section I .28Conduct of vessel in any condition of visibility.29|International Regulations for Preventing Collisions at Sea—Part B, Section I, Rule 6: Safe speed]]}}</ref> notwithstanding membership: Great Britain and its common law inheriting [[Commonwealth of Nations]],<ref name="common law2"/><ref name="common law"/> The United States,<ref name="Newton"/><ref name="The Colorado"/><ref name="Nacoochee"/> Florida,<ref>{{cite web |url=http://pascosheriff.com/websmart/Pasco/static/Boating%20Safety.htm |title=Boating Safety |quote=Excessive speed is a rate of speed greater than is reasonable or prudent without regard for conditions and hazards or greater than will permit a person to bring the boat to a '''stop within the assured clear distance ahead'''. |access-date=2013-08-27 |archive-url=https://web.archive.org/web/20130928054603/http://pascosheriff.com/websmart/Pasco/static/Boating%20Safety.htm |archive-date=2013-09-28 }}</ref> Hawaii,<ref>{{cite web |url=http://files.hawaii.gov/dlnr/dobor/rules/compiled/HAR244-Compiled.pdf |title=HAWAII ADMINISTRATIVE RULES, TITLE 13, DEPARTMENT OF LAND AND NATURAL RESOURCES, SUBTITLE 11, OCEAN RECREATION AND COASTAL AREAS, PART II, BOATING, CHAPTER 244 |publisher=The State of Hawaii |quote=HAR §13-244-7 Careless operation. No person shall operate any vessel in a careless or heedless manner so as to be grossly indifferent to the person or property of other persons, or at a rate of speed greater than will permit that person in the exercise of reasonable care to bring the vessel '''to a stop within the assured clear distance ahead'''.}}</ref> Illinois,<ref>{{cite web |url=http://www.ilga.gov/legislation/ilcs/ilcs4.asp?ActID=1826&ChapterID=49&SeqStart=8900000&SeqEnd=11100000 |title=Illinois Compiled Statutes, Ch. 625, Boat Registration and Safety Act. Sec. 5-1 |publisher=The State of Illinois |quote=Sec. 5-1. Careless operation. No person shall operate any watercraft in a careless or heedless manner so as to endanger any person or property or at a rate of speed greater than will permit him in the exercise of reasonable care to bring the watercraft '''to a stop within the assured clear distance ahead'''.}}</ref> Louisiana,<ref>{{cite web |url=http://law.justia.com/codes/louisiana/2006/41/92524.html |title=Louisiana Laws - RS 34:851.4—Careless operation |publisher=The State of Louisiana |year=2006}}</ref> Michigan,<ref>{{cite court |litigants=Torrez v. Willett, 366 Mich. 465 |vol=366 |reporter=Mich. |opinion=465 |court=[[Supreme Court of Michigan]] |date=May 18, 1962 |url=http://law.justia.com/cases/michigan/supreme-court/1962/366-mich-465-2.html |quote=Hereafter any motor boat, launch, or other water craft operated on the inland waters of this State or the waters connected with the Great Lakes. No such motor boat shall be operated on any of said waters in a reckless manner or at an excessive rate of speed so as to endanger the life or property of any person in or on said waters, having due regard to the presence of other boats, bathers or objects in or on such waters and of any other conditions then existing, and no person shall operate such motor boat on said waters at a rate of speed greater than will permit him '''to bring it to a stop within the assured clear distance ahead'''."}}</ref> Montana,<ref>{{cite web |url=http://leg.mt.gov/bills/mca/23/2/23-2-523.htm |title=§ 23-2-523(4). Prohibited operation and mooring -- enforcement |publisher=The State of Montana |access-date=August 6, 2013 |quote=§ 23-2-523(4): A person may not operate or knowingly permit a person to operate a motorboat or vessel at a rate of speed greater than will permit the person, in the exercise of reasonable care, to bring the vessel '''to a stop within the assured clear distance ahead'''. However, nothing in this part is intended to prevent the operator of a vessel actually competing in a regatta that is sanctioned by an appropriate governmental unit from attempting to attain high speeds on a marked racing course. |archive-date=June 29, 2013 |archive-url=https://web.archive.org/web/20130629092141/http://leg.mt.gov/bills/mca/23/2/23-2-523.htm |url-status=dead }}</ref> Oregon,<ref>{{cite web |url=http://www.oregonlaws.org/ors/830.315 |title=Oregon Revised Statues § 830.315 - Reckless operation speed |quote=§ 830.315(2) No person shall operate any boat at a rate of speed greater than will permit that person in the exercise of reasonable care to bring the boat '''to a stop within the assured clear distance ahead'''.}}</ref> Texas,<ref>{{cite web |url=http://tpwd.texas.gov/fishboat/boat/safety/safety_tips/ |title=Boating Safety: Operate at a Safe Speed |publisher=The State of Texas |quote=Excessive speed is a rate of speed greater than is reasonable or prudent without regard for conditions and hazards or greater than will permit a person to bring the boat '''to a stop within the assured clear distance ahead'''.}}</ref> and West Virginia.<ref>{{cite web |url=http://www.lrh.usace.army.mil/Portals/38/docs/recreation/Bluestone%20Boating%20Map.pdf |title=Article 7, Chapter 20 of the Official Code of West Virginia }}</ref>

Most state-issued and some Canadian driver handbooks instruct or mention the ACDA rule as required care or safe practice.<ref name="CDLM"/><ref name="CA Handbook">{{cite book |title=Driver Handbook |publisher=State of California: Department of Motor Vehicles |url=https://www.dmv.ca.gov/web/eng_pdf/dl600.pdf |chapter=Visual Search: How Well Can You Stop? |chapter-url=https://www.dmv.ca.gov/portal/dmv/detail/pubs/hdbk/scanning#hwcys |year=2015 |page=39 |quote='''If something is in your path, you need to see it in time to stop.''' Assuming you have good tires, good brakes, and dry pavement: At 55 mph, it takes about 400 feet to react and bring the vehicle to a complete stop. At 35 mph, it takes about 210 feet to react and bring the vehicle to a complete stop. Adjust your driving speed to the weather and road conditions (refer to the "Basic Speed Law" in the "Speed Limits" section). Turn on your lights during the day, if it is hard to see or you cannot see at least 1,000 feet ahead of you.}}</ref><ref name="AK Handbook">{{cite book |title=Alaska Driver Manual |publisher=State of Alaska |page=28 |url=http://www.doa.alaska.gov/dmv/dlmanual/dlman.pdf |quote=A person may not drive a vehicle upon a highway at a speed greater than will permit them to stop within the assured clear distance ahead}}</ref><ref name="NC Handbook">{{cite web |url=http://www.ncdot.gov/download/dmv/handbooks_NCDL_English.pdf |title=North Carolina Driver's Handbook |publisher=N.C. Division of Motor Vehicles |pages=51, 66 |quote=The faster you are moving, the farther ahead you must be able to see to allow enough distance for stopping ... Never drive at a speed at which you cannot stop within the distance you can see on the road ahead |access-date=2016-02-25 |archive-url=https://web.archive.org/web/20160304103344/http://www.ncdot.gov/download/dmv/handbooks_ncdl_english.pdf |archive-date=2016-03-04 }}</ref><ref>{{cite book |title=Driver's Manual |publisher=Oklahoma Department of Public Safety |pages=8–2 |url=http://www.dps.state.ok.us/dls/pub/ODM.pdf}}</ref><ref>{{cite book |title=Driver's Manual |publisher=Iowa Department of Transportation |page=39 |url=http://www.iowadot.gov/mvd/ods/dlmanual/dlmanual.pdf}}</ref><ref>{{cite book |title=Road Users Manual |publisher=Newfoundland and Labrador, Canada |page=49 |url=http://www.servicenl.gov.nl.ca/drivers/DriversandVehicles/driverlicensing/road_users_guide.pdf}}</ref><ref>{{cite book |title=Road Users Manual |publisher=Prince Edward Island, Canada |page=88 |url=http://www.gov.pe.ca/photos/original/tpw_dh_chap4.pdf}}</ref>

Explicit ACDA statutes and regulations,<ref name="49 CFR 392.14">{{Cite journal|url=https://www.law.cornell.edu/cfr/text/49/392.14 |title=49 CFR 392.14 - Hazardous conditions; extreme caution. |journal=[[Code of Federal Regulations|US Code of Federal Regulations]] |quote=Extreme caution in the operation of a commercial motor vehicle shall be exercised when hazardous conditions, such as those caused by snow, ice, sleet, fog, mist, rain, dust, or smoke, adversely affect visibility or traction. Speed shall be reduced when such conditions exist. If conditions become sufficiently dangerous, the operation of the commercial motor vehicle shall be discontinued and shall not be resumed until the commercial motor vehicle can be safely operated. Whenever compliance with the foregoing provisions of this rule increases hazard to passengers, the commercial motor vehicle may be operated to the nearest point at which the safety of passengers is assured.}}</ref> especially those of which create a citable driving or maritime offense, are aimed at preventing harm that could result from potentially negligent behavior—whereas the slightly more obscure common law ACDA doctrine is most easily invoked to remedy actual damages that have already occurred as a result of such negligence. Unsafe speed statutes are immune from being void for vagueness<ref name="void for vagueness"/> when they contain explicit ACDA clauses. Explicit and implicit ACDA rules govern millions of North American drivers.

====Universal standard of care====
Not all jurisdictions have applied the rule uniformly, most often differing over exceptions for specific "sudden emergencies". There has been an increased interest in the ACDA codified as a universal [[standard of care]]<ref name="275 U.S. 66"/><ref name="Holmes"/> that has been brought about by recent technological and social changes such as [[event data recorder]]s,<ref name="EDR">{{Cite journal|title=Federal Motor Vehicle Safety Standards; Event Data Recorders |date=December 12, 2012 |journal=Federal Register |url=https://www.federalregister.gov/articles/2012/12/13/2012-30082/federal-motor-vehicle-safety-standards-event-data-recorders}}</ref><ref>{{cite web |url=https://www.rimkus.com/uploads/pdfs/Event_Data_Recorder.pdf |title=Event Data Recorder Supported Vehicles |date=July 2015 |publisher=Rimkus Consulting Group, Inc. |access-date=2016-02-26 |archive-url=https://web.archive.org/web/20160311163851/http://www.rimkus.com/uploads/pdfs/event_data_recorder.pdf |archive-date=2016-03-11 }}</ref> [[dashcams]], [[self-driving cars]],<ref name="driver-less liability"/><ref name=":0" /> safe cities and multi-use movements,<ref>{{cite web |title=Urban Street Design Guide |date=8 April 2015 |publisher=[[National Association of City Transportation Officials]] |url=http://nacto.org/publication/urban-street-design-guide/ |quote=Streets comprise more than 80% of public space in cities, but they often fail to provide their surrounding communities with a space where people can safely walk, bicycle, drive, take transit, and socialize. Cities are leading '''the movement to redesign and reinvest in our streets as cherished public spaces for people, as well as critical arteries for traffic.'''}}</ref><ref name="CALTRANS multimodal">{{cite web |title=Caltrans Backs Innovative Street Design Guides to Promote Biking and Walking |publisher=California Department of Transportation |date=April 11, 2014 |url=http://www.dot.ca.gov/hq/paffairs/news/pressrel/14pr036.htm |quote=In an effort to support the construction of more multimodal local streets and roads, Caltrans today endorsed National Association of City Transportation Officials' (NACTO) guidelines that include innovations such as buffered bike lanes and improved pedestrian walkways.}}</ref><ref name="FHA multimodal">{{cite journal |title=How Does Transportation Affect Public Health? (FHWA-HRT-13-004) |author1=Eloisa Raynault |author2=Ed Christopher |journal=Public Roads |volume=76 |issue=6 |date=May 2013 |url=https://highways.dot.gov/public-roads/mayjune-2013/how-does-transportation-affect-public-health}}</ref><ref name="CDC multimodal">{{cite web |title=CDC Transportation Recommendations |publisher=[[Centers for Disease Control and Prevention]] |location=Atlanta, GA |url=https://www.cdc.gov/transportation/recommendation.htm |quote=The U.S. transportation system has been shaped by multiple policy inputs and concrete actions which have arisen from transportation and community planners, funding agencies and others at Federal, state and local levels. Today, the system is designed to move people and goods efficiently; however, there is a growing awareness across communities that transportation systems impact quality of life and health.|date=2018-02-07 }}</ref><ref name="EPA multimodal">{{cite web |title=Smart Growth and Transportation |publisher=[[United States Environmental Protection Agency]] |location=Washington, DC |url=http://www.epa.gov/smartgrowth/smart-growth-and-transportation |quote=Historically, transportation planners have overlooked the important role streets play in shaping neighborhoods. For decades, decisions about street size and design in many communities have focused on getting as many cars as possible through the streets as quickly as possible. Street design determines whether an area will be safe and inviting for pedestrians, bicyclists, and transit users, which affects the viability of certain types of retail, influences land values and tax receipts, and shapes overall economic strength and resilience.|date=2013-04-26 }}</ref><ref>{{cite web |title=Transportation |date=17 December 2019 |publisher=Smart Growth America |url=http://www.smartgrowthamerica.org/issues/transportation/ |quote=People want more transportation choices, whether it's to save money on gas, to get into shape by walking or biking to their destinations, or to have a more relaxing commute. Communities can provide these choices by making it easy for residents and visitors to drive, walk, bike, or take transit.}}</ref><ref>{{cite web |title=More Choices, Less Traffic |publisher=National Resource Defense Council |url=http://www.nrdc.org/transportation/choices.asp |quote=our auto-centric transportation system -- built for the previous century -- is increasing pollution and the nation's addiction to oil. After 50 plus years of building sprawl-spurring highways, experience shows that we cannot pave our way out of gridlock; instead, new road capacity is quickly filled up and the fiscal burden of its upkeep puts us back at square one. It is time to revamp America's ailing road and rail networks to create a competitive, 21st century solution. |access-date=February 28, 2016 |archive-date=March 4, 2016 |archive-url=https://web.archive.org/web/20160304162343/http://www.nrdc.org/transportation/choices.asp |url-status=dead }}</ref><ref>{{cite web |title=Transportation Choices for Sustainable Communities |url=http://transportchoice.org/|date=2014-01-17}}</ref><ref>{{cite web |title=What is universal access? |date=29 July 2021 |publisher=humantransport.org |url=http://www.humantransport.org/universalaccess/page3.html |quote=Universal access is the goal of enabling all citizens to reach every destination served by their public street and pathway system. Universal access is not limited to access by persons using automobiles. Travel by bicycle, walking, or wheelchair to every destination is accommodated in order to achieve transportation equity, maximize independence, and improve community livability.}}</ref><ref>{{cite book |title=Bicycle Blunders and Smarter Solutions |url=http://labreform.org/blunders/index.html |chapter=Blunders in Traffic Law and Enforcement |chapter-url=http://labreform.org/blunders/b6.html |publisher=LAB Reform}}</ref><ref>{{cite web |title=Assured Clear Distance Ahead and Vision Zero |date= October 2015 |publisher=BikeWalk NC |url=http://www.bikewalknc.org/2015/10/assured-clear-distance-ahead-and-vision-zero/}}</ref> and a movement to reduce claims by speeders against governments for "dangerous conditions" when operating speeds exceed a road's inferred design speed.<ref name="Kenworthy">{{cite book |title=Killer Roads: From Crash to Verdict |author=William Kenworthy |publisher=Lexis Law Pub |edition=2nd |date=January 1, 2000 |isbn=978-0327100164 }}</ref>

Collision liability has historically benefited the law profession by being cloaked as a mixture of fact and law, but with [[Event data recorder|EDR's]] precisely preserving "a state of facts" often repeated with differing trial outcomes, collisions are less a question of fact, but of law.<ref name="275 U.S. 66"/><ref name="Holmes"/><ref>{{cite court |litigants=Van Praag v. Gale |vol=107 |reporter=Cal |opinion=438 |court=[[Supreme Court of California]] |date=June 6, 1895 |quote= As a general proposition cases of negligence (to which those of contributory negligence form no exception) present a mixed question of law and fact, in which it devolves upon the court to say, as matter of law, what is or amounts to negligence, and upon the jury to say as matter of fact, whether or not in the particular case the facts in proof warrant the imputation of negligence. The court furnishes the standard; the jury adjusts the facts, and pronounces them as up to or falling short of the requirements of the standard.}}</ref><ref>{{cite court |litigants=Doyle v. Eschen |vol=5 |reporter=Cal.App |opinion=55 |court=[[California Court of Appeal]] |date=February 21, 1907 |url=https://casetext.com/case/doyle-v-eschen |access-date=February 2016 |quote=usually the consideration of negligence, including "contributory negligence," involves "a mixed question of law and fact, in which it devolves upon the court, to say, as a matter of law, what is or amounts to negligence, and upon the jury to say as matter of fact whether or not in the particular case the facts in proof warrant the imputation of negligence. The court furnishes the standard; the jury adjusts the facts and pronounces them as up to or falling short of the requirements of the standard. When, however, the facts are clearly settled, and the course which common prudence dictates can be readily discerned, the court should decide the case as matter of law.}}</ref><ref>{{cite court |litigants=Malinson v. Black |vol=83 |reporter=Cal.App.2d |opinion=375 |pinpoint=377-378 |court=[[California Court of Appeal]] |date=January 27, 1948 |url=http://law.justia.com/cases/california/court-of-appeal/2d/83/375.html |access-date=February 2016 |quote=Respondent testified that he came to a complete stop at the boulevard stop sign, surveyed the highway, saw that no cars were approaching from the right, and that the nearest car, presumably appellant's, approaching from the left, was at a distance of approximately 80 yards north of the intersection. Having concluded that he had plenty of time to safely cross the intersection, he proceeded in, looking straight ahead. ... we cannot declare such conduct to be negligence as a matter of law.}}</ref> Electronic access to precise EDR data and rulings with new ideological modeling tools, can now expose judges as consistent political advocates for differing special road user interests.<ref>{{cite web |title="Martin-Quinn" measures of judicial ideology |url=http://mqscores.berkeley.edu/ |publisher=University of California |archive-url=https://web.archive.org/web/20160307110257/http://mqscores.berkeley.edu/ |archive-date=2016-03-07 }}</ref><ref>{{cite web archived |title=Vehicles Lawyers Should Not Drive |author=Andrew Cabasso |date=September 3, 2015 |publisher=Lawyerist.com |url=https://lawyerist.com/86674/vehicles-lawyers-shouldnt-drive/2/ |quote=There must be some way to show clients you have won a lot of high-worth cases. How about an Audi A8, a Mercedes S-500, or a Lexus LS? Nope. Every lawyer has one of those. You need a car that shows that you are in a much higher tax bracket. You need a car that is worth more than your clients' homes. And they need to know it. Because when you hire "The Champ" (presumably the nickname you gave yourself), the client needs to know they will win their case and you will get a very nice contingency fee out of this one. |archive-url=https://web.archive.org/web/20150905165345/https://lawyerist.com/86674/vehicles-lawyers-shouldnt-drive/2/ |archive-date=2015-09-05}}</ref><ref name="Trans Lobbying">{{cite web |title=Influence & Lobbying: Transportation | publisher=[[OpenSecrets]] |url=https://www.opensecrets.org/industries/indus.php?ind=M |quote=The transportation sector is heavily involved in lobbying at the federal level, and expenditures have eclipsed $240 million each year from 2008 to 2012. ... two of the sector's most active lobbying clients, have attempted to influence legislation relating to '''transportation safety''' and security, travel taxes, and the authorization of federal funds for roads and railways.}}</ref><ref name="186 F.2d 562">{{cite court |litigants=United States v. National City Lines, Inc., et al |vol=186 |reporter=F.2d |opinion=562 |court=[[United States Court of Appeals for the Seventh Circuit]] |date=January 3, 1951 |url=https://casetext.com/case/united-states-v-national-city-lines-4 |access-date=2016 |quote=On April 9, 1947, nine corporations and seven individuals, constituting officers and directors of certain of the corporate defendants, were indicted on two counts, the second of which charged them with conspiring to monopolize certain portions of interstate commerce...the conspiracy to monopolize had consisted of a continuing agreement and concert of action upon the part of defendants under which the supplier defendants, [[Firestone Tire and Rubber Company|Firestone]], [[Standard Oil|Standard]], [[Phillips Petroleum Company|Phillips]], [[General Motors]] and [[Mack Trucks|Mack]], would furnish capital to defendants National, American and Pacific, and the latter companies would purchase and cause their operating companies to purchase from the supplier companies substantially all their requirements of tires, tubes and petroleum products; the capital made available by the supplier defendants would be utilized by National and Pacific, '''to purchase control of or financial interest in local public transportation systems, located in various states, when the securing of such control and interest would further the sale of and create an additional market for the products of the supplier defendants''' to the exclusion of products competitive therewith...as National and Pacific acquired local transportation systems in the other sections of the country, those markets would be allocated to and preempted by a company selling petroleum products in such sections...}}</ref> Furthermore, the law needs to be clear, precise, and uniform<ref name="uniform"/><ref name="red-blue"/> at a national level for the panoply of automobile manufacturers with the [[strict liability]] for their [[Computer programming|programming]] of law-abiding self-driving vehicles.<ref name="driver-less liability"/><ref name=":0" /> It is foreseeable that two self-driving car makes can collide because their algorithm of the law letter is different;<ref name="driver-less liability">{{cite web |title=Here's why lawyers are 'salivating' over self-driving cars |publisher= Business Insider Inc. |url=http://www.businessinsider.com/lawyers-are-salivating-over-driverless-cars-2015-12 |date=December 22, 2015 |quote=When, in the near future, a driverless car gets into an accident with another driverless car, it's going to be difficult to establish who is at fault. Is it the "driver," the car company, or even the programmer? ... "There's going to have to be some changes to the laws," David Strickland, former head of the National Highway Traffic Safety Administration, told Bloomberg. "There is no such thing right now that says the manufacturer of the automated system is financially responsible for crashes."}}</ref> a resolvable issue that has been troubling human drivers for decades. The ACDA is a standard with descriptive mathematics, much of which are used in reverse by road engineers when designing or re-engineering roads to a speed criteria—for which its users were expected to follow.<ref name="AASHTO"/>

==Determining the ACDA==
===Static ACDA===
====Forward "line-of-sight" distance====
{{Image frame |caption={{center|''[[Prima facie]]'' maximum speed ''vs.'' "line-of-sight" distance.<ref name="VA Table"/><br />''Permitted by good tires and clean, dry, level, pavement.''}}|content=
{{Graph:Chart|xAxisTitle=Assured Clear Distance Ahead [feet]|yAxisTitle=Prima Facie Maximum Speed [mph]|colors=blue,red|legend=Vehicle|y1Title=Cars|y2Title=Trucks|type=line
|x=27,44,63,85,109,135,164,195,229,265,303,344,387,433,481,531,584,639,696
|y1=10,15,20,25,30,35,40,45,50,55,60,65,70,75,80,85,90,95,100
|y2=9.6,14.2,18.6,23.1,27.6,31.9,36.3,40.7,45.1,49.5,53.8,58.2,62.6,67.0,71.3,75.6,80.0,84.4,88.7
<!--OCTAVE CODE
mu=0.525;,g=32.2;,t=1.5;,v=(sqrt(mu^2*g^2*t^2+2*mu*g.*D)-mu*g*t)*15/22   (mu=0.7 cars; 0.525 trucks) D="x array above"
Run online here:
https://octave-online.net/
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}}
}}
The range of visibility of which is the ''de facto'' ACDA, is usually that distance before which an ordinary person can see small hazards—such as a [[traffic cone]] or [[buoy]]—with [[20/20 vision]]. This distance may be attenuated by specific conditions such as [[Optical depth|atmospheric opacity]],<ref name="23 Cal. App. 2d 239">{{cite court
|litigants=Cannon v. Kemper, 23 Cal. App. 2d 239
|vol=23
|reporter=Official California Appellate Reports, 2nd Series
|opinion=239
|court=[[California courts of appeal|California Appellate Court]]
|publisher=Bancroft-Whitney; LexisNexis 
|date=October 21, 1937
|url=http://law.justia.com/cases/california/calapp2d/23/239.html
|access-date=2013-09-01
}} Driver traveling at 35 MPH when rain limited visibility to 25 feet held negligent when 65 feet were required to stop car on wet road. See [http://www.lexisnexis.com/clients/CACourts/ California Official Reports: Online Opinions]</ref> [[Glare (vision)|blinding glare]],<ref name="197 Cal. 82">{{cite court
|litigants=Hatzakorzian v. Rucker-Fuller Desk Co., 197 Cal. 82
|vol=197 
|reporter=Official California Reports
|opinion=82
|court=[[Supreme Court of California]]
|date=September 21, 1925 
|url=https://casetext.com/case/hatzakorzian-v-rucker-fuller-desk-co
|quote="Under the circumstances of the present case -- the narrowness of the unpaved portion of the highway, the darkness of the night and the '''blinding''' of Kennell by the '''glare of the lights''' reflected from the headlights of the approaching machine -- the highway over which Kennell was traveling was beset by danger of an extraordinary character from the time his vision became so obscured as to make it impossible for him to see plainly the road before him to the time that he struck the deceased. Thus the ordinary care with which Kennell was charged in driving his car over the highway required such an amount of such care as was commensurate with the exactions of the extraordinary dangerous circumstances under which he was then operating his car. The respective rights and duties of drivers of automobiles and other vehicles and of pedestrians have repeatedly been by the courts of this state clearly pointed out.."}}</ref> darkness,<ref name="CDLM">{{cite book |title=Commercial Driver License Manual 2005 |chapter=Section 2 – Driving Safely |url=https://www.fmcsa.dot.gov/registration/commercial-drivers-license/commercial-drivers-license-manual |chapter-url=https://www.fmcsa.dot.gov/sites/fmcsa.dot.gov/files/docs/2005%20CDL%20Driver%20Manual%20-July%202014%20-%20FINAL.pdf |pages=2–15, 2–19, 2–26, 13–1 |date=July 2014 |publisher=United States Department of Transportation |quote=[pg 2-15] ''' ''2.6.4 – Speed and Distance Ahead:'' ''' '''You should always be able to stop within the distance you can see ahead.''' Fog, rain, or other conditions may require that you slowdown to be able to stop in the distance you can see. ... [pg 2-19] ''' ''2.8.3 – Drivers Who Are Hazards: Vehicles may be partly hidden by blind intersections or alleys.'' ''' If you only can see the rear or front end of a vehicle but not the driver, then he or she can't see you. Be alert because he/she may back out or enter into your lane. '''Always be prepared to stop.''' ... [pg 2-26] ''' ''2.11.4 – Vehicle Factors: Headlights.'' ''' At night your headlights will usually be the main source of light for you to see by and for others to see you. You can't see nearly as much with your headlights as you see in the daytime. With low beams you can see ahead about 250 feet and with high beams about 350-500 feet. '''You must adjust your speed to keep your stopping distance within your sight distance.''' This means going slowly enough to be able to stop within the range of your headlights. ... [pg 13-1]''' ''13.1.2 – Intersections'' ''' As you approach an intersection: Check traffic thoroughly in all directions. '''Decelerate gently. Brake smoothly''' and, if necessary, change gears. If necessary, come to a complete stop (no coasting) behind any stop signs, signals, sidewalks, or stop lines maintaining a safe gap behind any vehicle in front of you. Your vehicle must not roll forward or backward. When driving through an intersection: Check traffic thoroughly in all directions. '''Decelerate ''and'' yield to any pedestrians and traffic in the intersection.''' Do not change lanes while proceeding through the intersection. Keep your hands on the wheel.}}</ref><ref name="236 Cal. App. 2d 555">{{cite court
|litigants=Bove v. Beckman, 236 Cal. App. 2d 555
|vol=236
|reporter=Official California Appellate Reports, 2nd Series
|opinion=555
|court=[[California courts of appeal|California Appellate Court]]
|publisher=Bancroft-Whitney; LexisNexis 
|date=Aug 16, 1965
|url=http://law.justia.com/cases/california/calapp2d/236/555.html
|access-date=2013-09-01
|quote="A person driving an automobile at 65 miles an hour on a highway on a dark night with his lights on low beam affording a forward vision of only about 100 feet was driving at a negligent and excessive speed which was inconsistent with any right of way that he might otherwise have had." (CA Reports Official Headnote #[8])}} See [http://www.lexisnexis.com/clients/CACourts/ California Official Reports: Online Opinions]</ref> [[Geometric design of roads|road design]],<ref name="6 Cal. App. 2d 224">{{cite court
|litigants=Falasco v. Hulen, 6 Cal. App. 2d 224
|vol=6
|reporter=Official California Appellate Reports, 2nd Series
|opinion=224
|court=[[California courts of appeal|California Appellate Court]]
|publisher=Bancroft-Whitney; LexisNexis 
|date=April 17, 1935
|url=http://law.justia.com/cases/california/calapp2d/6/224.html
|access-date=2013-09-01
|quote="'''Driving''' between 60 and 65 miles an hour over the brow of a hill, '''where one's view is obstructed and one cannot see''' what is on the opposite side of the hill '''for a sufficient distance to control the speed of his car, is an act showing a reckless disregard of the safety of others'''; and in said action, under the evidence, the jury was entitled to conclude either that defendant was driving at such a reckless rate of speed that he could not control the car, or that '''he was driving at such a high rate of speed that he did not perceive that the highway ahead of him afforded an unobstructed passage'''." (CA Reports Official Headnote #[9])}} See [http://www.lexisnexis.com/clients/CACourts/ California Official Reports: Online Opinions]</ref><ref name="22 Cal. App. 2d 636"/> and adjacent environmental hazards including civil and recreational activities,<ref name="189 Cal. 335"/> horse-drawn vehicle,<ref name="CVC 21759"/> ridden animal,<ref name="CVC 21759"/> livestock,<ref name="CVC 21759"/> deer,<ref name="deer"/> crossing traffic,<ref name="100 Cal. App. 2d 411">{{cite court
|litigants=Allin v. Snavely, 100 Cal. App. 2d 411 
|vol=100
|reporter=Official California Appellate Reports, 2nd Series
|opinion=411
|court=[[California courts of appeal|California Court of Appeal]]
|date=November 14, 1950
|url=http://law.justia.com/cases/california/calapp2d/100/411.html
|access-date=2013-07-27
|quote="A driver by insisting on his lawful right of way may violate the basic speed law as provided by Veh. Code, § 22350, and thus become guilty of negligence."(CA Reports Headnote #[2])}}</ref> and [[parking|parked cars]]. The ACDA may also be somewhat attenuated on roads with lower [[functional classification]].<ref name="FHWA">{{cite web |url=http://ntl.bts.gov/lib/23000/23100/23121/12SpeedCountsNumbers.pdf |title=Speeding Counts...''on all roads!'' |publisher=Federal Highway Administration (FHWA) |date=November 2000 |quote=Almost one of every three traffic fatalities is related to speeding, and speeding is a safety concern on all roads, regardless of their speed limits. However, much of the public concern about speeding has been focused on high-speed Interstates. The Interstate System actually has the best safety record of all roads and the lowest fatality rate per mile traveled. ... The difference in fatality rates by road classification reflects the difference in road design and use. The Interstate System is designed for high speeds, efficient movement of people and goods over long distances, with no at-grade intersections. Drivers have a clear view of the road, traffic, and signs. Collectors and local roads, however, are designed to provide more land access and lesser mobility. They may have sharp curves, steeper grades, and sight restrictions. The local road may also be shared by a high concentration of children and adult pedestrians, bicyclists, and an older user population. |access-date=2016-02-23 |archive-date=2013-10-16 |archive-url=https://web.archive.org/web/20131016055545/http://ntl.bts.gov/lib/23000/23100/23121/12SpeedCountsNumbers.pdf }}</ref><ref name="189 Cal. 335">
{{cite court
|litigants=Reaugh v. Cudahy Packing Co., 189 Cal. 335
|vol=189
|reporter=Official California Reports
|opinion=335
|court=[[Supreme Court of California]]
|date=July 27, 1922
|url=https://casetext.com/case/reaugh-v-cudahy-packing-co
|access-date=2016-02-23 
|quote=[The basic speed law] is but a reiteration of the rule, in statutory form, which '''has always been in force''' without regard to a statutory promulgation to the effect that drivers or operators of vehicles, and more particularly '''motor vehicles, must be specially watchful in anticipation of the presence of others at places where other vehicles are constantly passing, and where men, women, and children are liable to be crossing, such as corners at the intersections of streets or other similar places or situations where people are likely to fail to observe an approaching automobile.''' }} See [http://www.lexisnexis.com/clients/CACourts/ Official Reports Opinions Online]</ref><ref name="22 Cal. App. 2d 636">
{{cite court
|litigants=Riggs v. Gasser Motors, 22 Cal. App. 2d 636
|vol=22
|reporter=Official California Appellate Reports, 2nd Series
|opinion=636
|court=[[California courts of appeal|California Court of Appeal]]
|date=September 25, 1937 
|url=http://law.justia.com/cases/california/calapp2d/22/636.html
|access-date=July 22, 2013
|quote='''"It is common knowledge that intersecting streets in cities present a continuing hazard, the degree of hazard depending upon the extent of the use of the intersecting streets and the surrounding circumstances or conditions of each intersection. Under such circumstances the [[Speed limit#Basic rule|basic law]]...is always governing."''' }} See [http://www.lexisnexis.com/clients/CACourts/ Official Reports Opinions Online]</ref>
This is because the [[probability]] of spontaneous traffic increases proportionally to the density of road access points, and this density reduces the distance a person exercising [[ordinary care]] can be assured that a road will be clear; such reduction in the ACDA is readily apparent from the conditions, even when a specific access point or the traffic thereon is not.<ref name="139 Cal. App. 2d 65">
{{cite court
|litigants=Leeper v. Nelson, 139 Cal. App. 2d 65 
|vol=139
|reporter=Official California Appellate Reports, 2nd Series
|opinion=65
|court=[[California courts of appeal|California Court of Appeal]]
|date=Feb 6, 1956
|url=http://law.justia.com/cases/california/calapp2d/139/65.html 
|access-date=2013-07-27 
|quote='''"The operator of an automobile is bound to anticipate that he may meet persons or vehicles at any point of the street, and he must in order to avoid a charge of negligence, keep a proper lookout for them and keep his machine under such control as will enable him to avoid a collision with another automobile driven with care and caution as a reasonably prudent person would do under similar conditions."'''}} See [http://law.justia.com/cases/california/calapp2d/91/142.html Huetter v. Andrews, 91 Cal. App. 2d 142], [https://casetext.com/case/berlin-v-violett Berlin v. Violett, 129 Cal.App. 337], [https://casetext.com/case/reaugh-v-cudahy-packing-co Reaugh v. Cudahy Packing Co., 189 Cal. 335], and [http://courts.ca.gov/opinions-slip.htm Official Reports Opinions Online]</ref>{{refn|For this reason, full [[Geometric design of roads#Corner sight distance|corner sight distance]] is almost never required for individual driveways in urban high-density residential areas, and street parking is commonly permitted within the [[Right-of-way (transportation)|right-of-way]]. |group="Note" |name="ACDA governed by cornersight"}} Furthermore, even though a through-driver may typically presume all traffic will stay assuredly clear when required by law, such driver may not take such presumption when circumstances provide actual knowledge under ordinary care that such traffic cannot obey the law.<ref name="139 Cal. App. 2d 65"/> During times of darkness, commercial vehicles can see ahead about 250 feet with low beams, and about 350–500 feet with high beams.<ref name="CDLM"/> This clear distance corresponds to a maximum safe speed of 52&nbsp;mph and 65-81&nbsp;mph respectively on dry pavement with good tires,<ref name="VA Table"/><ref name="AAA headlights">{{cite news |last1=McKernan |first1=Megan |title=AAA Tests Shine High-Beam on Headlight Limitations |url=https://newsroom.aaa.com/2015/05/aaa-tests-shine-high-beam-headlight-limitations/ |access-date=3 July 2018 |agency=AAA Automotive Research Center |publisher=NewsRoom.AAA.com |date=13 May 2015 |quote=AAA's test results suggest that [[Headlamp#Tungsten-halogen|halogen headlights]], found in over 80 percent of vehicles on the road today, may fail to safely illuminate unlit roadways at speeds as low as 40 mph. ...high-beam settings on halogen headlights...'''may only provide enough light to safely stop at speeds of up to 48 mph''', leaving drivers vulnerable at highway speeds...Additional testing found that while the advanced headlight technology found in [[Headlamp#High-intensity discharge (HID)|HID]] and [[Headlamp#LED|LED]] [[Headlamp|headlights]] illuminated dark roadways 25 percent further than their halogen counter parts, they still may fail to fully illuminate roadways at speeds greater than 45 mph. High-beam settings on these advanced headlights offered significant improvement over low-beam settings, lighting distances of up to 500 feet (equal to 55 mph). Despite the increase, '''even the most advanced headlights fall 60 percent short of the [[sight distance]] that the full light of day provides.'''}}</ref> which is attenuated further by [[Geometric design of roads#Crest Curves|convex]] and [[Geometric design of roads#Alignment|lateral road curvature]]; safe speed is always dynamic. Non-commercial vehicles have even shorter lighting distances.<ref name="AAA headlights"/> Drivers commonly drive the [[speed limit|maximum posted speed limit]] at night, often in violation of the ACDA rule<ref name="AAA headlights"/><ref name="236 Cal. App. 2d 555"/><ref name="245 Mich. 88"/><ref name="23 Cal. App. 2d 239"/> and this shows up in accident data.<ref name="NHTSA Night&Day">{{cite web |url=https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/810637 |title=Passenger Vehicle Occupant Fatalities by Day and Night – A Contrast |last1=Varghese |first1=Cherian |last2=Shankar |first2=Umesh |agency=National Center for Statistics and Analysis |publisher=National Highway Traffic Safety Administration |location=Washington, DC |date=May 2007 |quote=The passenger vehicle occupant fatality rate at nighttime is about three times higher than the daytime rate. ...'''The data shows a higher percentage of passenger vehicle occupants killed in speeding-related crashes at nighttime.'''}}</ref><ref name="Leibowitz&Herschel"/>
<!-- Create SAVT [https://en.wikipedia.org/wiki/Template:Graph:Chart]<ref name="Hoffmann & Mortimer"/><ref name="Maddox"/> -->

=====Intersections=====
{{multiple image
| align             = right
| caption_align     = center
| direction         = vertical
| width             = 400
| header            = Visual limits of drivers entering intersection from a stop
| footer            = <br />As a vehicle creeps into an intersection, the lateral perspective diminishes until head-on looming motion is the more insightful of the two. Both lateral and looming motion may also combine somewhat to enhance detection according to [[Gestalt Theory]], permitting they are both observable.
| caption1          = Head-on car speed ''vs.'' [[Visual acuity#Subtended angular velocity detection threshold .28SAVT.29|detection distance of looming motion]].<ref name="Maddox"/><br />''For an onlooker without assistance of lateral movement.''<ref name="83 Cal. App. 2d 377"/><ref name="43 Cal.2d 626"/>
| image1            = {{Graph:Chart|xAxisTitle=Oncoming Car Speed [mph]|yAxisTitle=Detection Distance of Motion [feet]|legend=SAVT Limit Range |colors=green,yellow,orange |y2Title=convention (0.0275)|y1Title=lowerbound (0.0117)|y3Title=upperbound (0.0397)|type=line
|x=0.5,1,2.5,5,10,15,20,25,30,35,40,45,50,55,60,65,70,75,80
|y2=12.288,17.635,28.125,39.887,56.489,69.217,79.944,89.392,97.934,105.788,113.097,119.962,126.456,132.631,138.532,144.191,149.636,154.890,159.972
|y1=19.159,27.261,43.259,61.251,86.674,106.175,122.612,137.093,150.184,162.221,173.426,183.949,193.902,203.368,212.413,221.088,229.435,237.489,245.279
|y3=10.091,14.583,23.349,33.156,46.985,57.584,66.515,74.381,81.492,88.029,94.114,99.829,105.234,110.374,115.286,119.996,124.52,128.902,133.132
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 | alt2=Graph: Head-on car speed plotted against detection distance of looming motion 
}}
| caption2          = Lateral car speed ''vs.'' [[Visual acuity#Lateral motion|detection distance of lateral motion]].<ref name="Lappin et. al.">{{cite journal |title=Spatial and temporal limits of motion perception across variations in speed, eccentricity, and low vision. |first1=Joseph S. | last1=Lappin |first2=Duje | last2=Tadin |first3=Jeffrey B. |last3=Nyquist |first4=Anne L. |last4=Corn |journal=Journal of Vision |volume=9 |number=30 |pages=30.1–14 |date=January 2009 |doi=10.1167/9.1.30 |pmid=19271900 |quote=Displacement thresholds for peripheral motion were affected by acuity limits for speeds below 0.5 degrees/s. [0.0087 radians/s] | name-list-style=vanc|doi-access=free }}</ref><br />''For an onlooker without assistance of looming movement.''<ref name="83 Cal. App. 2d 377"/><ref name="43 Cal.2d 626"/>
| image2            = {{Graph:Chart|xAxisTitle=Lateral Car Speed [mph]|yAxisTitle=Detection Distance of Motion [feet]|legend=Setback Distance |colors=red,purple,blue |y1Title=Setback 4 feet|y2Title=Setback 15 feet|y3Title=Setback 30 feet|type=line
|x=0.5,1,1.5,2,2.5,3,3.5,4,4.5,5,10,15,20,25,30,35,40,45,50,55,60,65,70,75,80
|y1=17.921,25.658,31.551,36.506,40.863,44.799,48.416,51.781,54.941,57.928,82.020,100.493,116.063,129.778,142.176,153.576,164.186,174.152,183.577,192.541,201.106,209.321,217.226,224.853,232.229
|y2=32.239,47.997,59.734,69.516,78.082,85.797,92.874,99.448,105.614,111.439,158.311,194.180,224.387,250.985,275.022,297.121,317.686,336.999,355.263,372.633,389.229,405.145,420.460,435.236,449.526
|y3=40.358,64.478,81.769,95.994,108.368,119.467,129.619,139.032,147.847,156.165,222.878,273.792,316.622,354.312,388.361,419.656,448.775,476.116,501.970,526.556,550.044,572.569,594.242,615.151,635.372

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 | alt2=Graph: Setback distance plotted against detection distance of lateral motion 
}}
}}
As a corollary to the rule that drivers generally must not pose an "immediate hazard" upon where or when they cannot assure such distance ahead is clear, it follows that others may presume that no vehicle is posing an "immediate hazard" from beyond where they can see with proper lookout. Where there are cross roads or side roads with view obstructions, the assured clear distance terminates at the closest path of potential users of the roadway until there is such a view which assures the intersection will remain clear. In such situations, approach speed must be reduced in preparation for entering or crossing a road or intersection or the unmarked pedestrian crosswalks<ref>{{cite web |url=https://www.dmv.ca.gov/portal/dmv/detail/pubs/vctop/vc/d1/275 |title=California Vehicle Code §275(a) |publisher=The State of California |quote="Crosswalk" is...That portion of a roadway included within the prolongation or connection of the boundary lines of sidewalks at intersections where the intersecting roadways meet at approximately right angles, except the prolongation of such lines from an alley across a street. |access-date=June 10, 2015 |archive-date=June 11, 2015 |archive-url=https://web.archive.org/web/20150611044747/https://www.dmv.ca.gov/portal/dmv/detail/pubs/vctop/vc/d1/275 |url-status=dead }}</ref><ref>{{cite web |url=https://www.dmv.ca.gov/portal/dmv/detail/pubs/vctop/vc/d11/c5/21950 |title=California Vehicle Code §21950(a)&(c) |publisher=The State of California |quote='''The driver of a vehicle shall yield the right-of-way to a pedestrian crossing the roadway''' within any marked crosswalk or '''within any unmarked crosswalk at an intersection''', except as otherwise provided in this chapter. ... The driver of a vehicle approaching a pedestrian within any marked or '''unmarked crosswalk''' shall exercise all due care and '''shall reduce the speed of the vehicle''' or take any other action relating to the operation of the vehicle as necessary to safeguard the safety of the pedestrian. |access-date=June 10, 2015 |archive-date=June 11, 2015 |archive-url=https://web.archive.org/web/20150611130527/https://www.dmv.ca.gov/portal/dmv/detail/pubs/vctop/vc/d11/c5/21950 |url-status=dead }}</ref> and bike paths<ref>{{cite web |url=https://www.dmv.ca.gov/portal/dmv/detail/pubs/vctop/vc/d1/231.6 |title=California Vehicle Code §231.6(a) |publisher=The State of California |quote=A "bicycle path crossing" is ...That portion of a roadway included within the prolongation or connection of the boundary lines of a bike path at intersections where the intersecting roadways meet at approximately right angles. |access-date=June 10, 2015 |archive-date=June 11, 2015 |archive-url=https://web.archive.org/web/20150611013130/https://www.dmv.ca.gov/portal/dmv/detail/pubs/vctop/vc/d1/231.6 |url-status=dead }}</ref> they create because of potential hazards.<ref name="J. Stannard Baker"/><ref name="106 Cal. App. 2d 294">{{cite court |litigants=Grasso v. Cunial, 106 Cal. App. 2d 294 |vol=106 |reporter=California Official Reports, 2nd Series |opinion=294 |court=[[California courts of appeal|California Court of Appeal]] |date=August 27, 1951 |url=http://www.lexisnexis.com/clients/CACourts/ |quote=Nor is a plaintiff required to yield the right of way to one a considerable distance away whose duty it is to slow down in crossing an intersection. See [http://www.lexisnexis.com/clients/CACourts/ Official Reports Opinions Online]}}</ref><ref name="179 Cal. 349">{{cite court |litigants= Whitelaw v. McGilliard,179 Cal. 349 |vol=179 |reporter=Official California Reports |opinion=349 |court=[[Supreme Court of California]] |date=December 4, 1918 |url=https://casetext.com/case/whitelaw-v-mcgilliard |quote=The rule regarding right of way does not impose upon the person crossing the street the duty of assuming that the other will continue across an intersecting street without slowing down, as required by law. See [http://www.lexisnexis.com/clients/CACourts/ Official Reports Opinions Online]}}</ref><ref name="213 Cal. 644"/><ref>{{cite court |litigants=Fitts v. Marquis, 127 Me. 75 |vol=127 |reporter=Maine Reporter |opinion=75 |court=[[Supreme Judicial Court of Maine]] |date=March 15, 1928 |url=https://casetext.com/case/fitts-v-marquis |quote=If a situation indicate collision, the driver, who can do so by the exercise of ordinary care, should avoid doing injury, though this involve that he waive his right of way. The supreme rule of the road is the rule of mutual forbearance.}}</ref><ref name="Human Factors"/> This [[jurisprudence]] arises in-part because of the known difficulty in [[Stadiametric rangefinding|estimating the distance]] and velocity of an approaching vehicle,<ref name="Human Factors"/><ref name="83 Cal. App. 2d 377"/><ref name="43 Cal.2d 626"/> which is [[Psychophysics|psychophysically]] explained by its small [[angular size]] and belated divergence from an [[asymptotically]] null [[Differentiation of trigonometric functions#Differentiating the inverse cotangent function|rate]] of expansion, which is beyond the [[Visual acuity#Subtended angular velocity detection threshold .28SAVT.29|subtended angular velocity detection threshold (SAVT)]] limits of [[visual acuity]]<ref name="Weinberger">{{cite journal |title=Conjecture on the Visual Estimation of Relative Radial Motion |author=Hershel Weinberger |journal=[[Nature (journal)|Nature]] |volume=229 |issue=5286 |page=562 |date=19 February 1971 |doi=10.1038/229562a0 |pmid=4925353 |bibcode=1971Natur.229..562W |s2cid=4290244 |doi-access=free }}</ref><ref>{{cite journal |title=Spatial and temporal limits of motion perception across variations in speed, eccentricity, and low vision. |author1=Joseph S. Lappin |author2=Duje Tadin |author3=Jeffrey B. Nyquist |author4=Anne L. Corn |journal=Journal of Vision |volume=9 |number=30 |pages=30.1–14 |date=January 2009 |doi=10.1167/9.1.30 |pmid=19271900 |quote=Displacement thresholds for peripheral motion were affected by acuity limits for speeds below 0.5 degrees/s.|doi-access=free }}</ref><ref name="Nature">{{cite journal |title=Perceiving visual expansion without optic flow |author1=Paul R. Schrater |author2=David C. Knill |author3=Eero P. Simoncelli |journal=[[Nature (journal)|Nature]] |volume=410 |issue=6830 |pages=816–819 |date=12 April 2001 |doi=10.1038/35071075 |pmid=11298449 |bibcode=2001Natur.410..816S |s2cid=4406675 |quote=When an observer moves forward in the environment, the image on his or her retina expands. The rate of this expansion conveys information about the observer's speed and the time to collision...this rate might also be estimated from changes in the size (or scale) of image features...we show,...observers can estimate expansion rates from scale-change information alone, and that '''pure scale changes can produce motion after-effects.''' These two findings suggest that '''the visual system contains mechanisms that are explicitly sensitive to changes in scale.'''}}</ref><ref name="Hoffmann & Mortimer">{{cite journal |title=Scaling of relative velocity between vehicles |author1=Errol R. Hoffmann |author2=Rudolf G. Mortimer |journal=Accident Analysis & Prevention |volume=28 |issue=4 |date=July 1996 |pages=415–421 |issn=0001-4575 |doi=10.1016/0001-4575(96)00005-X |quote=Only when the subtended angular velocity of the lead vehicle exceeded about 0.003 rad/s were the subjects able to scale the relative velocity |pmid=8870768}}</ref><ref name="Maddox">{{cite journal |title=Looming Threshold Limits and Their Use in Forensic Practice |author1=Michael E. Maddox |author2=Aaron Kiefer |journal=Proceedings of the Human Factors and Ergonomics Society Annual Meeting |volume=50 |number=1 |pages=700–704 |date=September 2012 |doi=10.1177/1071181312561146 |s2cid=109898296 |quote=A number of laboratory researchers have reported values of the looming threshold to be in the range of 0.003 radian/sec. Forensic practitioners routinely use elevated values of the looming threshold, e.g., 0.005-0.008, to account for the complexity of real-world driving tasks. However, only one source has used data from actual vehicle accidents to arrive at a looming threshold – and that value, 0.0275 rad/sec, is an order of magnitude larger than that derived from laboratory studies. In this study, we examine a much broader range of real-world accident data to obtain an estimate of the reasonable upper end of the looming threshold. The results show a range of 0.0397 to 0.0117 rad/sec... }}</ref> by way of the [[Stevens' power law]]<ref name="Hoffmann & Mortimer"/> and [[Weber–Fechner law]], until the vehicle may be dangerously close; [[subjective constancy]] and the [[visual angle illusion]]<ref>{{cite journal |title=Transforming vision into action |author=Melvyn A. Goodale |journal=Vision Research |volume=51 |number=13 |date=1 July 2011 |pages=1567–1587 |doi=10.1016/j.visres.2010.07.027 |pmid=20691202 |issn=0042-6989 |doi-access=free }}</ref> may also play a role.{{refn| While the [[Gestalt effect]] is generally valuable in processing visual information, [[ambiguity]] such as that specific to approaching distant vehicles can also lead to problematic [[multistable perception]], erroneous [[filling-in]], and spectacular failure such as the [[Ebbinghaus illusion]], [[Delboeuf illusion]], and [[Ponzo illusion]]. Such honest [[human error]] insidiously arises through [[unconscious inference]]s from insufficient, distracting, or illusory information—it is especially important to foresee such hazard at intersections.|group="Note"}}{{refn|Under the worst-case scenario, a driver will make decisions alone based upon the "looming motion" of oncoming headlights or silhouette of an anonymous vehicle, which must reach a certain proximity in order to exceed the visual expansion acuity threshold, <math>\dot{\theta}_t</math>. Given a vehicle of size <math>S</math> and distance <math>x</math>, the [[visual angle]] is: <math>\theta=2\arctan{\left (\tfrac{S}{2x} \right)}</math>. Its [[Differentiation of trigonometric functions#Differentiating the inverse tangent function|derivative]] with respect to distance is <math>\tfrac{d\theta}{dx}=\tfrac{-4S}{S^2+4x^2}</math>. An approaching vehicle of constant [[velocity]] <math>v</math> will decrease the distance at [[Rate (mathematics)|rate]] <math>\tfrac{dx}{dt}=-v</math>. The time rate of visual expansion is obtained from the rate at which the [[subtended angle]] grows with decreased distance, multiplied by the rate at which the distance lessens with time: <math>\tfrac{d\theta}{dt}=\tfrac{\mathrm{d}\theta}{\mathrm{d}x}\cdot\tfrac{\mathrm{d}x}{\mathrm{d}t}</math>. It follows that <math>\frac{4S \cdot v}{S^2+4x^2} \gtrsim \dot{\theta_{t}}</math>. Hence, an approaching vehicle's looming motion is not perceivable until <math>x \lesssim \sqrt{\frac{S \cdot v}{\dot{\theta_{t}}}-\frac{S^2}{4}}</math>, where the {{math|{{sfrac|S<sup>2</sup>|4}}}} term is omitted with [[small-angle approximation]]. The [[units of measurement]] for size, distance, and velocity variables must be of the same system (i.e. multiply by {{math|{{sfrac|22|15}}}} to convert [[Miles per hour|MPH]] to [[Foot per second|ft/s]] or {{math|{{sfrac|5|18}}}} to convert [[Kilometres per hour|km/h]] to [[Metre per second|m/s]] or {{math|{{sfrac|&pi;|180}}}} to convert [[Degree (angle)|deg]] to requisite [[radians|rad]]). [http://www.visualexpert.com/Resources/rearendcollision.html Read more about this topic]|group="Note"}} Vehicles that are approaching an intersection from beyond the [[Visual acuity#Subtended angular velocity detection threshold (SAVT)|SAVT]] limit cannot be reliably distinguished between moving or parked, though they may be traveling at such an imprudent speed as to pose an immediate hazard. In this circumstance, it is impossible for the entering driver to have fair notice that his or her contemplated conduct is forbidden by such hazard,<ref name="269 US 385">{{cite court |litigants=[[Connally v. General Construction Co.]] |vol=269 |reporter=[[United States Reports]] |opinion=385 |pinpoint=391 |court=[[Supreme Court of the United States]] |date=January 4, 1926 |url=https://supreme.justia.com/cases/federal/us/269/385/case.html |access-date=February 2016 |quote=That the terms of a penal statute creating a new offense must be sufficiently explicit to inform those who are subject to it what conduct on their part will render them liable to its penalties is a well recognized requirement, consonant alike with ordinary notions of fair play and the settled rules of law, and a statute which either forbids or requires the doing of an act in terms so vague that men of common intelligence must necessarily guess at its meaning and differ as to its application violates the first essential of due process of law.}}</ref><ref name="43 Cal.2d 626"/> and any legal expectation to the contrary would implicate violating the [[vagueness doctrine]] of the [[US Constitution]].<ref name="269 US 385"/>{{refn| The [[overbreadth doctrine]] is also implicated whereby to avoid the risk of legal consequences for using blind intersections for which there is no fair notice of other traffic bringing a prohibition of its use into effect, persons with no alternative route are dissuaded from the liberty of free movement, expression, and to peacefully assemble. Hence the law's effects are thereby far broader than intended or than the U.S. Constitution permits. Furthermore, as insufficient intersectional sight-distance is often symptomatic of old, urban high-density neighborhoods, with multiple tenant households saturating narrow street parking,—predominately lower social-economic environments—entire classes of people may be unequally discouraged from even leaving their houses. The through-driver is not adversely affected in this regard, by being compelled to slow down as to be able to stop to avoid collision with entering car or pedestrian as required by law. |group="Note"}} It is the duty of the through-driver to decelerate<ref name="CDL">{{cite book |title=California Commercial Driver Handbook (2014-2015) |chapter=Section 13: On-Road Driving |chapter-url=https://www.dmv.ca.gov/portal/dmv/detail/pubs/cdl_htm/sec13?projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d&projectid=34cc355c-5dc2-49e1-86d5-ca94968e3e3d |url=https://www.dmv.ca.gov/portal/wcm/connect/42c566ef-31ac-4df2-a8ed-480619084886/comlhdbk.pdf?MOD=AJPERES |pages=2–19, 13–2 |publisher=California Department of Motor Vehicles |date=2015 |quote=[pg 2-19] 2.6.4 – '''Speed and Distance Ahead[:]''' You should always be able to stop within the distance you can see ahead. Fog, rain, or other conditions may require that you slow down to be able to stop in the distance you can see. ... [pg 13-2]'''13.1.2 – Intersections''' As you approach an intersection: • Check traffic thoroughly in all directions. • '''Decelerate gently.''' • '''Brake smoothly''' and, if necessary, change gears. • If necessary, come to a complete stop (no coasting) behind any stop signs, signals, sidewalks, or stop lines maintaining a safe gap behind any vehicle in front of you. • Your vehicle must not roll forward or backward. Note: Do not enter the intersection if there is insufficient space to clear it. When driving through an intersection: •Check traffic thoroughly in all directions. •'''Decelerate ''and'' yield to any pedestrians and traffic in the intersection.''' •Do not change lanes while proceeding through the intersection. •Keep your hands on the wheel. |access-date=March 15, 2016 |archive-date=April 14, 2016 |archive-url=https://web.archive.org/web/20160414085247/https://dmv.ca.gov/portal/wcm/connect/42c566ef-31ac-4df2-a8ed-480619084886/comlhdbk.pdf?MOD=AJPERES |url-status=dead }}</ref><ref name="106 Cal. App. 2d 294"/><ref name="179 Cal. 349"/><ref name="213 Cal. 644"/> and apply the ACDA principle specifically to the intersection.<ref name="CDLM"/><ref name="189 Cal. 335"/><ref name="175 Cal. 497"/><ref name="22 Cal. App. 2d 636"/><ref name="100 Cal. App. 2d 411"/>
See [[Assured Clear Distance Ahead#Table of detection thresholds|Table of detection thresholds]].

{{Hidden begin|titlestyle = text-align: left; font-size:100%; padding-right:1em;|contentstyle = text-align: left; font-size:100%; padding-left:1em; 
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|title=Technical ACDA Theory of Intersections
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When approaching an un-signalized intersection controlled by a [[stop sign]], the assured clear distance ahead is:

:<math>
ACDA_{si} = V \left( \sqrt{\frac{2d_i}{a_i}} + t_{pc} \right)
</math>

Normal acceleration "{{math|a<sub>i</sub>}}" for a passenger vehicle from a stop up to 20&nbsp;mph is about 0.15g, with more than 0.3g being difficult to exceed.<ref name="J. Stannard Baker"/> The distance "{{math|d<sub>i</sub>}}" is the sum of the measured [[Stop and yield lines|limit line]] setback distance—which is typically regulated by a [[Manual on Uniform Traffic Control Devices]], at often between 4 and 30 feet in the United States<ref name="23 CFR 603">{{cite web |url=http://www.ecfr.gov/cgi-bin/text-idx?SID=a2583ef3fa3a41e5b157549f8dd705ab&mc=true&node=pt23.1.655&rgn=div5#se23.1.655_1603 |title=Title 23, Code of Federal Regulations, Part 655.603 |publisher=US Government Publishing Office |quote=The MUTCD approved by the Federal Highway Administrator is the national standard for all traffic control devices installed on any street, highway, or bicycle trail open to public travel in accordance with 23 U.S.C. 109(d) and 402(a)...Where State or other Federal agency MUTCDs or supplements are required, they shall be in substantial conformance with the National MUTCD.}}</ref><ref name="CAMUTCD">{{cite book |chapter-url=http://www.dot.ca.gov/hq/traffops/engineering/mutcd/ca_mutcd2014.htm |title=California MUTCD 2014 |publisher=California Department of Transportation |chapter=3B.16.10 |page=681 |quote=Chapter 3B.16.10: If used, stop and yield lines should be placed a minimum of 4 feet in advance of the nearest crosswalk line at controlled intersections...In the absence of a marked crosswalk, the stop line or yield line should be placed at the desired stopping or yielding point, but should not be placed more than 30 feet or less than 4 feet from the nearest edge of the intersecting traveled way.}}</ref><ref name="CAHDM">{{cite book |title=California Highway Design Manual |publisher=California Department of Transportation |chapter=405.1 |pages=400–14 |year=2012 |chapter-url=http://www.dot.ca.gov/hq/oppd/hdm/hdmtoc.htm |quote=Chapter 405.1: Set back for the driver of the vehicle on the crossroad shall be a minimum of 10 feet plus the shoulder width of the major road but not less than 15 feet.}}</ref>—and the [[crosswalk]], [[Parallel parking|parking lane]], and [[road shoulder]] width. A vehicle accelerating from a stop travels this distance in time {{math| t<sub>i</sub>{{=}}{{radical|{{frac|2d<sub>i</sub>|a<sub>i</sub>}}}}}} while through traffic travels a distance equal to their speed multiplied by that time. The time {{math|t<sub>pc</sub>}}, for the stopped motorist, is the sum of perception time and the time required to actuate an automatic transmission or shift to first gear which is usually between {{math|{{frac|1|2}}}} to one second.<ref name="AASHO"/>
{{hidden end}}

====ACDA as a function of horizontal sight distance====
Horizontal clearance is measured from the edge of the traveled way to the bottom of the nearest object, tree trunk or shrub foliage mass face, plant setback, or mature growth.<ref name="AASHTO">{{cite book |title=A Policy on Geometric Design of Highways and Streets |edition=6th |year=2011 |publisher=American Association of State Highway and Transportation Officials |isbn=978-1560515081 |url=https://bookstore.transportation.org/collection_detail.aspx?ID=110}}</ref><ref name="CDOT"/> Horizontal sight distance is not to be confused with the clear recovery zone which provides hazardous vegetation set-back to allow errant vehicles to regain control, and is exclusive to a mowed and limbed-up forest which can allow adequate sight distance, but unsafe recovery.<ref name="CDOT"/> The height and lateral distance of plants restrict the horizontal sight distance, at times obscuring wildlife which may be spooked by an approaching vehicle and run across the road to escape with their [[herd]].<ref name="deer">{{Cite journal |title = Targeting mitigation efforts: The role of speed limit and road edge clearance for deer–vehicle collisions |doi = 10.1002/jwmg.712 |journal =The Journal of Wildlife Management |date=2014 |volume=78 |issue = 4 |pages=679–688 |quote=speed limit reduction and road edge clearance are both powerful mitigation tools to reduce the number of [[Deer–vehicle collisions]].|last1 = Meisingset |first1 = Erling L |last2 = Loe |first2 = Leif E |last3 = Brekkum |first3 = Øystein |last4 = Mysterud |first4 = Atle |bibcode = 2014JWMan..78..679M }}</ref><ref name="CDOT"/> This principle also applies to approaching vehicles and pedestrians at uncontrolled intersections and to a lesser degree by un-signalized intersections controlled by a [[yield sign]]. Horizontal sight distance "{{math|d<sub>hsd</sub>}}" affects the ACDA because the time {{math|t<sub>i</sub>{{=}}{{sfrac|d<sub>hsd</sub>|V<sub>i</sub>}}}} it takes for an intercepting object, animal, pedestrian, or vehicle with speed "{{math|V<sub>i</sub>}}" to transverse this distance after emerging from the proximate edge of lateral visibility affords a vehicle with speed "{{math|V}}" a clear distance of "{{math|V*t<sub>i</sub>}}". Thus, the assured clear intercept distance "{{math|ACDA<sub>si</sub>}}" is:

:<math>
ACDA_{si}=\frac{V d_{hsd}}{V_i}
</math>

The faster one drives, the farther down-road an interceptor must be in order to be able to transverse the horizontal sight distance in time to collide, however this says nothing of whether the vehicle can stop by the end of this type of assured clear distance. Equating this distance to the total stopping distance and solving for speed yields one's maximum [[Assured Clear Distance Ahead#ACDA rule-specific case generalized to the Basic Speed Law|safe speed]] as purely dictated by the horizontal sight distance.

===Dynamic "following" distance===
The ACDA may also be dynamic as to the moving distance past which a motorist can be assured to be able to stay clear of a foreseeable dynamic hazard—such as to maintain a distance as to be able to safely swerve around a bicyclist should he succumb to a fall—without requiring a full stop beforehand, if doing so could be exercised with [[due care]] towards surrounding traffic. Quantitatively this distance is a function of the appropriate time gap and the operating speed: {{math|d<sub>ACDA</sub>{{=}}t<sub>gap</sub>&sdot;<var>v</var>}}. The assured clear distance ahead rule, rather than being subject to exceptions, is not really intended to apply beyond situations in which a vigilant ordinarily prudent person could or should anticipate.<ref name="75 ALR.3d 327"/> A common way to violate the dynamic ACDA is by [[tailgating]].

===Measurement===
The most accurate way to determine the ACDA is to directly measure it. Whereas this is impractical, [[Geometric design of roads#Profile|sight distance formulas]] can be used with less direct measurements as rough baseline estimates. The [[empirical]] assured clear distance ahead calculated with [[computer vision]], [[range finding]], [[traction control]], and [[Geographic information system|GIS]], such as by properly [[Computer programming|programming]] computer hardware used in [[autonomous cars]], can be recorded to later produce or color baseline ACDA and safe speed maps for accident investigation, traffic engineering, and show disparities between safe speed and 85th percentile "operating" speed.<ref name="computer vision">{{cite news |url=https://www.nytimes.com/2015/11/15/magazine/the-dream-life-of-driverless-cars.html |title=Sightlines/The Dream Life of Driverless Cars |author=Geoff Manaugh |work=[[The New York Times]] |page=MM68 |date=November 15, 2015 |quote=One of the most significant uses of 3-D scanning in the years to come will not be by humans at all but by autonomous vehicles.}}</ref> Self-driving cars<ref name=":0" /><ref name="rules">{{cite news |url=https://www.nytimes.com/2015/09/02/technology/personaltech/google-says-its-not-the-driverless-cars-fault-its-other-drivers.html |title=Google's Driverless Cars Run Into Problem: Cars With Drivers |author1=Matt Richtel |author2=Conor Dougherty |work=[[The New York Times]] |page=A1 |date=September 2, 2015 |quote=Google's fleet of autonomous test cars is programmed to follow the letter of the law. But it can be tough to get around if you are a stickler for the rules. ... One Google car, in a test in 2009, couldn't get through a four-way stop because its sensors kept waiting for other (human) drivers to stop completely and let it go. The human drivers kept inching forward, looking for the advantage—paralyzing Google's robot. ... "It's always going to follow the rules, I mean, almost to a point where human drivers who get in the car and are like 'Why is the car doing that?'" said Tom Supple, a Google safety driver during a recent test drive on the streets near Google's Silicon Valley headquarters. ...the technology, like Google's car, drives by the book. It leaves what is considered the safe distance between itself and the car ahead. ...Dmitri Dolgov, head of software for Google's Self-Driving Car Project, said that one thing he had learned from the project was that human drivers needed to be "less idiotic." ... The laser system mounted on top of the driverless car sensed that a vehicle coming the other direction was approaching the red light at higher-than-safe speeds. The Google car immediately jerked to the right in case it had to avoid a collision. }}</ref> may have a higher safe speed than human driven vehicles for a given ACDA where computer perception-reaction times are nearly instantaneous.

===Discretion===
The Assured Clear Distance Ahead can be subjective to the baseline estimate of a [[ordinary care|reasonable person]] or be predetermined by law. For example, whether one should have reasonably foreseen that a road was not assuredly clear past 75–100 meters because of tractors or livestock which commonly emerge from encroaching blinding vegetation is on occasion dependent on societal experience within the locale. In certain urban environments, a straight, traffic-less, through-street may not necessarily be assuredly clear past the entrance of the nearest [[Geometric design of roads#Effects of insufficient sight distance|visually obstructed intersection]] as law.<ref name="189 Cal. 335"/><ref name="22 Cal. App. 2d 636"/><ref name="139 Cal. App. 2d 65"/><ref name="Human Factors"/> Within the assured clear distance ahead, there is certainty that travel will be free from obstruction which is exclusive of a failure to appreciate a hazard. Collisions generally only occur within one's assured clear distance ahead which are "unavoidable" to them such that they have zero comparative negligence including [[Act of God|legal acts of god]] and abrupt unforeseeably wanton negligence by another party. Hazards which penetrate one's proximate edge of clear visibility and compromise their ACDA generally require evasive action.

Drivers need not and are not required to precisely determine the maximum safe speed from real-time mathematical calculations of sight distances and stopping distances for their particular vehicle.<ref name="83 Cal. App. 2d 377">{{cite court |litigants=Malinson v. Black, 83 Cal. App. 2d 377 |vol=83 |reporter=Official California Appellate Reports, Second Series |opinion=377 |court=[[California courts of appeal|California Appellate Court]] |publisher=Bancroft-Whitney; LexisNexis |date=January 27, 1948 |url=http://law.justia.com/cases/california/court-of-appeal/2d/83/375.html |quote=It is apparent that plaintiff misjudged the speed of the truck and was mistaken as to his ability to cross Anaheim Street in front of it with safety. However, every mistake of judgment is not negligence, for mistakes are made even in the exercise of ordinary care. [http://www.lexisnexis.com/clients/CACourts/ See Official Reports Online.]}}</ref> Motor vehicle operators of average intelligence<ref name="Holmes">{{cite book |title=The Common Law |author=Oliver Wendell Holmes Jr. |publisher=[[Little, Brown and Company]] |date=1881 |page=108,122,123 |chapter=Lecture III—D. Liability for unintended Harm is determined by what would be Blameworthy in Average man |chapter-url=https://archive.org/stream/commonlaw00holmuoft#page/108/mode/2up |quote=The standards of the law are standards of general application. The law takes no account of the infinite varieties of temperament, intellect, and education which make the internal character of a given act so different in different men. ... [Page 122] the averment that the defendant has been guilty of negligence ... that his alleged conduct does not come up to the legal standard. ... the question whether the court or the jury ought to judge of the defendant's conduct is wholly unaffected by the accident, ... it is entirely possible to give a series of hypothetical instructions adapted to every state of facts which it is open to the jury to find. ... the court may still take their opinion as to the standard. ... [page 123] ...supposing a state of facts often repeated in practice, is it to be imagined that the court is to go on leaving the standard to the jury forever? ... if the jury is, on the whole, as fair a tribunal as it is represented to be, the lesson which can be got from that source will be learned.... the court will find ... the conduct complained of usually is or is not blameworthy, ... or '''it will find the jury oscillating to and fro, and will see the necessity of making up its mind for itself.''' There is no reason why any other such question should not be settled, as well as that of liability for stairs with smooth strips of brass upon their edges.|title-link=The Common Law (Holmes) |author-link=Oliver Wendell Holmes, Jr }}</ref><ref name="47 Cal.App.3d 164">{{cite court |litigants=Fox v. City and County of San Francisco, 47 Cal.App.3d 164 |vol=47 |reporter=Official California Appellate Reports, 3rd Series |opinion=164 |court=[[California courts of appeal|California Appellate Court]] |date=April 14, 1975 |publisher=Bancroft-Whitney; LexisNexis |url=http://law.justia.com/cases/california/court-of-appeal/3d/47/164.html |quote=drivers with mental disabilities are required to exercise the ordinary care required of an adult without such disability. [http://www.lexisnexis.com/clients/CACourts/ See Official Reports Online.]}}</ref> are constantly required to utilize their [[Eye–hand coordination|kinesthetic memory]] in all sorts of driving tasks including every time they brake to a full stop at a stop line in a panoply of conditions.<ref name="156 Cal.App.2d 374"/><ref name="Gibson&Crooks">{{cite journal |title=A Theoretical Field-Analysis of Automobile-Driving |author1=James J. Gibson |author2=Laurence E. Crooks |journal=The American Journal of Psychology |volume=51 |issue=3 |pages=453–471 |date=July 1938 |doi=10.2307/1416145 |issn=0002-9556 |oclc=473102987 |jstor= 1416145 }}</ref> Like throwing a softball, one does not have to mathematically calculate a trajectory or firing solution in order to hit a target with repeated accuracy. During the earliest stages of [[action learning|learning how to drive]], one develops a memory of when to start braking (how long it takes) from various speeds in order to stop at the limit line.<ref name="Gibson&Crooks"/> While there may be a degree of variance of such skill in seasoned drivers, they generally do not have the discretion in engaging in a behavior such as driving a speed above which no reasonable minds might differ as to whether it is unsafe or that one could come to a stop within the full distance ahead.<ref name="213 Cal. 644"/><ref name="47 Cal.App.3d 164"/>

====Seconds of distance to stop rule====
Drivers and law enforcement alike can apply elementary level arithmetic<ref>{{cite web |url=http://www.corestandards.org/assets/CCSSI_Math%20Standards.pdf |title=Common Core State Standard for Mathematics |publisher=Common Core State Standards Initiative |page=27 |quote=See 4th grade math level |access-date=February 22, 2016 |archive-date=October 19, 2013 |archive-url=https://web.archive.org/web/20131019052731/http://www.corestandards.org/assets/CCSSI_Math%20Standards.pdf |url-status=dead }}</ref> towards a [[rule of thumb]] to estimate minimal stopping distance in terms of how many seconds of travel ahead at their current speed. For speed "{{math|<var>v</var>}}" in miles per hour, this rule of thumb is as follows:

:::<math>\color{Sepia}{t\approx\frac{v}{20} + 1 \quad \text{(seconds of distance to stop rule)}}</math>

If this distance is greater than the ACDA, they need to decelerate. While most experienced drivers develop a broad [[intuition]] required by everyday braking,<ref name="Gibson&Crooks"/> this rule of thumb can still benefit some to recalibrate expectations for rare hard braking, particularly from high speeds. Additional simple corrections can be made to compensate for the environment and driving ability. Read more about the [[Assured Clear Distance Ahead#Seconds of distance to stop rule 2|Seconds of Distance to Stop Rule]].

==ACDA rule-specific case generalized to the Basic Speed Law==
The ACDA distances are a principal component to be evaluated in the determination of the maximum safe speed (V<sub>BSL</sub>) under the basic speed law, without which the maximum safe speed cannot be determined. As mathematical statements are more precise than verbal statements alone,<ref name="Hand rule">{{cite court |litigants=[[United States v. Carroll Towing Co.]] |author1=[[Learned Hand]] |author2=[[Harrie B. Chase]] |author3=[[Jerome Frank]] |vol=159 |reporter=[[Federal Reporter#Federal Reporter.2C Second Series|Federal Reporter, Second Series]] |opinion=169 |pinpoint=173 |court=[[United States Court of Appeals for the Second Circuit]] |date=January 9, 1947 |url=http://law.justia.com/cases/federal/appellate-courts/F2/159/169/1565896/ |access-date=February 2016 |quote=Since there are occasions when every vessel will break from her moorings, and since, if she does, she becomes a menace to those about her; the owner's duty, as in other similar situations, to provide against resulting injuries is a function of three variables: (1) The probability that she will break away; (2) the gravity of the resulting injury, if she does; (3) the burden of adequate precautions. Possibly it serves to bring this notion into relief to state it in algebraic terms: '''if the probability be called P; the injury, L; and the burden, B; liability depends upon whether B is less than L multiplied by P: i. e., whether B > PL.''' [https://h2o.law.harvard.edu/cases/1287 See ruling here]}}</ref> the relation of the ACDA as a [[subset]] of the basic speed rule for land based vehicles may be objectively quantified as follows:

:<math>
V_{BSL}= \begin{cases}
 \sqrt{(\mu +e)^2 g^2 t_{prt}^2+ 2 (\mu + e) g d_{ACDA_s} } - (\mu+e) g t_{prt}, & \text{if } V_{ACDA_s} \le V_{ACDA_{si1}} \text{ or } V_{ACDA_{si2}} \text{ or } V_{ACDA_d} \text{ or } V_{cs} \text{ or } V_{cl}\\
\\
2 g (\mu + e) (\frac{d_{hsd}}{v_i}-t_{prt}), & \text{if } V_{ACDA_{si1}} < V_{ACDA_s} \text{ or } V_{ACDA_{si2}} \text{ or } V_{ACDA_d} \text{ or } V_{cs} \text{ or } V_{cl}\\
\\
2 g (\mu + e )\left(\sqrt{\frac{2 d_{sl}}{a_i}}+t_{pc}-t_{prt}\right), & \text{if } V_{ACDA_{si2}} < V_{ACDA_s} \text{ or } V_{ACDA_{si1}} \text{ or } V_{ACDA_d} \text{ or } V_{cs} \text{ or } V_{cl}\\
\\
 \frac{d_{ACDA_d}}{t_g}, & \text{if } V_{ACDA_d}< V_{ACDA_s} \text{ or } V_{ACDA_{si1}} \text{ or } V_{ACDA_{si2}} \text{ or } V_{cs} \text{ or } V_{cl} \\
\\
 \sqrt{ \frac{(\mu+e) g r}{1-\mu e}}, & \text{if } V_{cs}<V_{ACDA_s} \text{ or } V_{ACDA_{si1}} \text{ or } V_{ACDA_{si2}} \text{ or } V_{ACDA_d} \text{ or } V_{cl} \\
\\
 V_{cl}, & \text{if } V_{cl}< V_{ACDA_s} \text{ or } V_{ACDA_{si 1}} \text{ or } V_{ACDA_{si 2}} \text{ or } V_{ACDA_d} \text{ or } V_{cs}
\end{cases}

</math>

The value of the variable "e" is the [[sine]] of the [[angle]] of inclination of the road's [[slope]]. For a level road this value is zero, and for [[Small-angle approximation|small angles]] it approximates the road's percent [[Grade (slope)|grade]] divided by one hundred.
:<math>
e = \sin(\theta) \approx \theta \approx \tan(\theta) = \frac{\%\text{grade}}{100}
</math>

{{refn|
In most jurisdictions, [[judicial notice]] shall be taken of the [[braking distance#Total stopping distance|total stopping distance]], and such notice is therefore logically and substantively taken of the maximum speed permitted to brake within the stopping distance as applied to the ACDA. The latter is merely the [[inverse function]] of the former. Furthermore, fundamental mathematical relationships are themselves subject to judicial notice.

: <math>V_{ACDA(s)}=\sqrt{\mu^2 g^2 t_{prt}^2+ 2 \mu g d_{ACDA_s} } - \mu g t_{prt}</math>

For example, using the <math>\mu=0.7</math> and <math>t_{prt}=1.5</math> values that produced [http://law.lis.virginia.gov/vacode/46.2-880/ Code of Virginia § 46.2-880 Tables of speed and stopping distances], one simply obtains the same velocities that produced the [[braking distance#Total stopping distance|stopping distance]] in the statute:

[[Metric system|Metric]] ([[International System of Units|SI]]) – Speed in [[km/h]] from distance in [[Metre|meters]]:

: <math>V_{ACDA} \approx \sqrt{1372.3+ 177.8 d_{ACDA} } - 37.0</math>

[[United States customary units|US customary]] – Speed in [[Miles per hour|MPH]] from distance in [[Foot (unit)|feet]]:
: <math>V_{ACDA} \approx \sqrt{529.8+ 20.9 d_{ACDA} } - 23.0</math>
|group="Note" |name="BSL formula example"}}

The maximum velocity permitted by the Assured Clear Distance Ahead is controlling of safe speed (V<sub>BSL</sub>) for only the top and two cases. Safe speed may be greater or less than the actual [[speed limit|legal speed limit]] depending upon the conditions along the road.<ref name="J. Stannard Baker">{{cite book |title=Traffic Accident Investigator's Manual for Police |edition=2 |author=J. Stannard Baker |publisher=The Traffic Institute, Northwestern University |year=1963 |pages=43–48 |lccn=62-20895}}
</ref>

{{refn| Safe Speed will be outputted in the same terms as the input units. Entering a distance in feet and an acceleration in terms of feet/s<sup>2</sup> will produce a safe speed in terms of feet/second. To convert to miles per hour, multiply by {{math|{{sfrac|22|15}}}}. Entering distance and acceleration in terms of meters will output a speed in meters per second, which may be converted to kilometers per hour by multiplying by a {{math|{{sfrac|18|5}}}} (or 3.6) factor. |group="Note" |name="Converting to familiar units"}}

See reference [[assured clear distance ahead#Derivations|''V''<sub>BSL</sub> derivations]] for basic physics explanation.

===ACDA: forward line-of-sight===
For the top case, the maximum speed is governed by the assured clear "line-of-sight", as when the "following distance" aft of forward traffic and "steering control" are both adequate. Common examples include when there is no vehicle to be viewed, or when there is a haze or fog that would prevent visualizing a close vehicle in front. This maximum velocity is denoted by the case variable <math>V_{ACDA_s}</math>, the [[coefficient of friction|friction coefficient]] is symbolized by <math>\mu</math>—and itself a function of the [[Treadwear rating|tire type]] and [[road slipperiness|road conditions]], the distance <math>d_{ACDA_s}</math> is the static ACDA, the constant <math>g</math> is the [[Gravity of Earth|acceleration of gravity]], and interval <math>t_{prt}</math> is the [[Mental chronometry|perception-reaction time]]—usually between 1.0 and 2.5 seconds.<ref name="Taoka">{{cite journal |last1=Taoka |first1=George T. |title=Brake Reaction Times of Unalerted Drivers |journal=ITE Journal |volume=59 |issue=3 |pages=19–21 |date=March 1989 |url=http://www.ite.org/membersonly/itejournal/pdf/jca89a19.pdf }}{{Dead link|date=May 2019 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref name="Olsen&Sivak">{{cite journal |title=Perception-response time to unexpected roadway hazards |author1=Paul L. Olson |author2=Michael Sivak |journal=Human Factors |volume=28 |issue=1 |pages=91–96 |date=February 1986 |doi= 10.1177/001872088602800110 |pmid=3710489 |s2cid=13632058 |quote=Perception-response (PR) time, the time from the first sighting of an obstacle until the driver applies the brakes, is an important component of stopping sight distance. ... The results indicate a 95th percentile PR time of about 1.6 s for both age groups.}}</ref>

See [[Assured Clear Distance Ahead#Table of ACDA: forward line-of-sight|Table of safe speed versus forward line-of-sight]]

===ACDA: horizontal line-of-sight===
The second case describes the relationship of horizontal sight distance on safe speed. It is the maximum speed at which a vehicle can come to a full stop before an object, with speed V<sub>i</sub>, can intercept after having emerged and traveled across the horizontal sight distance "d<sub>hsd</sub>". Urban and residential areas have horizontal sight distances that tend to be closely obstructed by parked cars, utility poles, street furnishing, fencing, signage, and landscaping, but have slower intercepting speeds of children, pedestrians, backing cars, and domestic animals. These interceptors combined with dense usage results in collisions that are more probable and much more likely to inflict harm to an outside human life. In rural areas, swift-moving spooked wildlife such as [[deer]],<ref name="deer"/> [[elk]], [[Moose#Vehicle collisions|moose]], and [[pronghorn|antelope]] are more likely to intercept a roadway at over 30&nbsp;mph (48&nbsp;km/h). Wildlife will frequently transit across a road before a full stop is necessary, however collisions with large [[Game (hunting)|game]] are foreseeably lethal, and a driver generally has a duty not to harm his or her passengers. The foreseeable intercept speed or defectively designed horizontal sight distance may vary "reasonably" with [[judicial discretion]].

See [[Assured Clear Distance Ahead#Table of ACDA: horizontal line-of-sight|Table of safe speed versus horizontal line-of-sight]]

===ACDA: intersectional setback===
This third case regards safe speed around un-signalized intersections where a driver on an uncontrolled through street has a duty to slow down in crossing an intersection and permit [[stop sign|controlled]] drivers to be able pass through the intersection without danger of collision.<ref name="213 Cal. 644">{{cite court |litigants=Page v. Mazzei, 213 Cal. 644 |vol=213 |reporter=Official California Reports |opinion=644 |court=[[Supreme Court of California]] |date=21 September 1931 |url=https://casetext.com/case/page-v-mazzei |quote=Where a car has actually entered an intersection before the other approaches it, the driver of the first car has the right to assume that he will be given the right of way and be permitted to pass through the intersection without danger of collision. He has a right to assume that the driver of the other car will obey the law, slow down, and yield the right of way, if slowing down be necessary to prevent a collision. ( Keyes v. Hawley, 100 Cal. App. 53, 60 [279 Pac. 674].) Nor is a plaintiff required to yield the right of way to one a considerable distance away whose duty it is to slow down in crossing an intersection. See [http://www.lexisnexis.com/clients/CACourts/ Official Reports Opinions Online]}}</ref><ref name="227 La. 932">{{cite court |litigants=Booth v. Columbia Casualty Company |vol=227 |reporter=La. |opinion=932 |court=[[Supreme Court of Louisiana]] |date=April 25, 1955 |url=https://law.justia.com/cases/louisiana/supreme-court/1955/227-la-932-0.html |quote=The plaintiff having pre-empted the intersection had the right to proceed and under the wellsettled jurisprudence the automobile which first enters an intersection has the right of way over an approaching automobile and the driver who does not respect this legal right of the automobile which first entered the intersection to proceed through in safety, is negligent, even though the car thereafter entering the intersection is being driven on a right of way street.}}</ref> The driver on the through street must anticipate and hence not approach at an unsafe speed which would prevent another driver from being able to enter while traffic was some distance away, or would be unsafe to a driver who has already established control of the intersection under a prudent acceleration a<sub>i</sub>, from a stop at a limit line a distance d<sub>sl</sub> away.<ref name=AASHO>{{cite book |title=A Policy on Geometric Design of Rural Highways |publisher=American Association of State Highway and Traffic Officials |date=1969 |page=394 |quote=Where an obstruction, which cannot be removed except at prohibitive cost, fixes the vertices of the sight triangle at points that are less than the safe stopping distances from the intersection, vehicles may be brought to a stop (after sighting other vehicles on the intersecting road) only if they are traveling at a speed appropriate to the available sight distance.}}</ref>

===ACDA: following distance===
The pedantic fourth case applies when the dynamic ACDA "following distance" (''d''<sub>ACDA<sub>''d''</sub></sub>) is less than the static ACDA "line-of-sight" distance (''d''<sub>ACDA<sub>s</sub></sub>). A classic instance of this occurs when, from a visibility perspective, it would be safe to drive much faster were it not for a slower-moving vehicle ahead. As such, the dynamic ACDA is governing the basic speed rule, because in maintaining this distance, one cannot drive at a faster speed than that matching the forward vehicle. The "time gap" ''t''<sub>g</sub> or "time cushion" is the time required to travel the dynamic ACDA or "following distance" at the [[operating speed]]. Circumstances depending, this cushion might be manifested as a [[two-second rule]] or three-second rule.

See [[Assured clear distance ahead#Table of following distances|Table of 2-second following distances]]

===Critical speed===
In the fifth case, critical speed ''V''<sub>cs</sub> applies when road curvature is the factor limiting safe speed. A vehicle which exceeds this speed will [[slip angle|slide]] out of its lane. Critical speed is a function of curve [[radius]] ''r'', [[Cant (road/rail)|superelevation]] or banking ''e'', and friction coefficient ''μ'';<ref name="J. Stannard Baker"/> the constant ''g'' again is the acceleration of gravity. However, most motorists will not tolerate a lateral acceleration exceeding 0.3g (''μ''&nbsp;=&nbsp;0.3) above which many will panic.<ref name="Glennon-Hill">{{cite book |title=Roadway Safety and Tort Liability |edition=2 |publisher=Lawyers & Judges Publishing Company, Inc. |author1=John C. Glennon |author2=Paul F. Hill |page=293 |url=https://books.google.com/books?id=LmqrDaOwn3kC&pg=PA293|isbn=9781930056947 |year=2004 }}</ref> Hence, critical speed may not resemble loss of control speed.<ref name="Glennon-Hill"/> Attenuated "side" friction coefficients are often used for computing critical speed.<ref name="CDOT">{{cite book |url=http://www.dot.ca.gov/hq/oppd/hdm/hdmtoc.htm |title=Highway Design Manual |chapter=Geometric Design And Structure Standards |chapter-url=http://www.dot.ca.gov/hq/oppd/hdm/pdf/english/chp0200.pdf |pages=200–1, 200–2, 200–3, 200–4, 200–7, 200–10, 200–11, 200–20 |publisher=California Department of Transportation}}</ref> The formula is frequently approximated without the denominator for low angle banking which may be suitable for nearly all situations except the tightest radius of highway onramps.<ref name="CDOT"/><ref>{{cite web |url=http://www.cadzone.com/manuals/crash-crime/crash9/Program_Commands/recon_menu/Critical_Speed_calc.htm |title=Critical Speed Calculator |publisher=The CAD Zone. Inc. |date=2015}}</ref> The principle of critical speed is often applied to the problem of [[traffic calming]], where curvature is both used to govern maximum road speed, and used in [[traffic circles]] as a device to force drivers to obey their [[Duty of care|duty]] to slow down when approaching an intersection.<ref name="106 Cal. App. 2d 294"/><ref name="179 Cal. 349"/>

See [[assured clear distance ahead#Table of critical speeds|Table of curvatures and critical speeds]]

===Surface control===
The bottom case is invoked when the maximum velocity for surface control V<sub>cl</sub> is otherwise reached. Steering control is independent from any concept of clear distance ahead. If a vehicle cannot be controlled so as to safely remain within its lane above a certain speed and circumstance, then it is irrelevant how assuredly clear the distance is ahead. Using the example of the previous case, the safe speed on a curve may be such that a driver experiences a lateral acceleration of less than 0.3g despite that the vehicle may not slide until it experiences 0.8g. [[Speed wobble]], [[aquaplaning|hydroplaning]], [[roll center]], [[fishtailing]], [[jackknifing|jackknife]] tendencies, [[potholes]], [[washboarding]], [[frost heaving]],<ref name="Montana v. Stanko">{{cite court |litigants=State of Montana v. Rudy Stanko |court=[[Supreme Court of Montana]] |date=23 December 1998 |url=https://caselaw.findlaw.com/mt-supreme-court/1110919.html |access-date=February 2016 |quote=the road was narrow, there were hills and curves which presented some degree of obstruction to the view ahead, and there was an occasional frost heave on the surface of the road.   A reasonable speed under these circumstances would require a calculation of sight distances and stopping distances for the particular vehicle.... The arresting officer described in detail the roadway where Stanko was operating his vehicle at 85 miles per hour.   The roadway was very narrow with no shoulders.   There were frost heaves on the road which caused the officer's vehicle to bounce.   The highway had steep hills, sharp curves, and multiple no-passing zones.   There were numerous ranch and field access roads in the area which ranchers use for bringing hay to their cattle.   The officer testified that at 85 miles per hour, there was no way for Stanko to stop in the event there had been an obstruction on the road beyond the crest of a hill.   In the officer's judgment, driving a vehicle at the speed of 85 miles per hour on the stretch of road in question posed a danger to the rest of the driving public.}}</ref> and [[tire speed rating]] are other factors limiting V<sub>cl</sub>.

==Safe speed==
Safe speed is the maximum speed permitted by the basic speed law and negligence doctrine. Safe speed is not the same as the 85 percentile [[operating speed]]<ref>{{cite web |url=https://safety.fhwa.dot.gov/speedmgt/ref_mats/fhwasa10001/ |title=Speed Concepts: Informational Guide |publisher=US Department of Transportation |quote='''Operating speed''' - the speeds at which vehicles are observed operating during free flow conditions. Free flow speeds are those observed from vehicles whose operations are unimpeded by traffic control devices (e.g., traffic signals) or by other vehicles in the traffic stream. The 85th percentile of the distribution of observed speeds is the most frequently used measure of the operating speed.}}</ref> used by traffic engineers in establishing speed zones.<ref name="J. Stannard Baker"/><ref name="23 CFR 603"/><ref name="23 CFR 625"/><ref name="US MUTCD"/> Fog, snow, or ice can create conditions where most people drive too fast, and [[Multiple-vehicle collision|chain reaction accidents]] in such conditions are examples of where large groups of drivers collided because they failed to reduce speed for the conditions.<ref name="J. Stannard Baker"/><ref name="mass crash">{{cite news |url=https://www.theguardian.com/uk-news/2013/sep/05/car-pileup-sheppey-bridge-kent |title='All you could hear was cars crashing': 120-car pile-up on Sheppey bridge |author=Maev Kennedy |date=September 6, 2013 |work=[[The Guardian]] |quote=the probable cause of the accident was "stupid driving". ... "It's really bad to travel too close to the car in front in good conditions and if you do it in foggy conditions it's an absolute recipe for disaster."}}</ref> The speeds at which most people drive can only be a very rough guide to safe speed,<ref name="J. Stannard Baker"/> and an illegal or negligent custom or practice is not in itself excusable.<ref name="60 Cal. App. 764">{{cite court |litigants=Reinders v. Olsen, 60 Cal. App. 764 |vol=60 |reporter=California Appellate Reports |opinion=764 |court=California Appellate Court |date=February 13, 1923 |url=https://casetext.com/case/reinders-v-olsen |quote=the fact of knowledge on the part of plaintiff relating to the "custom" or, rather, practice, of automobile drivers ... no such practice could be binding on plaintiff so as to excuse defendant from violating the statute in that regard, provided that such act was the proximate cause of the accident. See [http://www.lexisnexis.com/clients/CACourts/ Official Reports Opinions]}}</ref><ref name="Holmes"/><ref name="McCormick et al.">{{cite journal |title=Comparative perceptions of driver ability–A confirmation and expansion |author1=Iain A. McCormick |author2=Frank H. Walkey |author3=Dianne E. Green |journal=[[Accident Analysis & Prevention]] |volume=18 |number=3 |pages=205–208 |date=June 1986 |doi=10.1016/0001-4575(86)90004-7 |pmid=3730094 |issn=0001-4575 |quote=a substantial majority of drivers, up to 80%, would rate themselves above average on a number of important characteristics}}</ref><ref name="275 U.S. 66"/> Safe speed approximates the inferred [[design speed]] adjusted for environmental alterations and vehicle and person specific factors when V<sub>ACDA<sub>s</sub></sub> is the limiting factor.<ref>{{cite web |url=https://safety.fhwa.dot.gov/speedmgt/ref_mats/fhwasa10001/ |title=Speed Concepts: Informational Guide |publisher=US Department of Transportation |quote='''Inferred design speed''' – the maximum speed for which all critical design-speed-related criteria are met at a particular location.}}</ref> The [[Solomon curve]] concept can create an [[approach-avoidance conflict]] within the driver who wishes neither to drive faster than is lawful and the conditions allow nor have an unsafe speed discrepancy between other vehicles on the road; it is never legal to go faster than the speed limit, and unilaterally reducing the risk of the latter can lead to a mass crash caused by the former.<ref name="mass crash"/>
<!--Driving too fast for conditions more dangerous that exceeding posted speed limit  https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/811090       https://safety.fhwa.dot.gov/speedmgt/ref_mats/fhwasa10001/-->

===Relationship of posted speed limits to the explicitness of driver care standard===
[[File:2005 winter road dipped beam.jpg|thumb|Distance seen with [[ECE Regulations|ECE]] light by night]]

Many people are challenged by the concept of ''unsafe speed'' because they find it vague and arbitrary.<ref name="void for vagueness"/> It is well known that people instead resolve such challenges by [[attribute substitution]],<ref name="kahneman_aer">{{cite journal |last=Kahneman |first=Daniel |date=December 2003 |title=Maps of Bounded Rationality: Psychology for Behavioral Economics |journal= American Economic Review |volume=93 |issue=5 |pages=1449–1475 |doi=10.1257/000282803322655392 |issn=0002-8282 |citeseerx=10.1.1.194.6554 |s2cid=15131441 }}</ref> which in this case can mean simply emulating the behaviors of others. In accord with the [[cultural theory of risk]], indeed a substantial part of a driver's [[risk perception]] comes from comparing their contemplated conduct to the behavior of others; this includes the safeness of a given speed, notwithstanding the actual risk. As a result of this uncorrected vagueness, group behavior can often be in opposition to safe speed and still be governing a hazardous posted speed limit. By federal law, posted speed limits are generally within 5&nbsp;mph of the 85th-percentile speed of free-flowing traffic.<ref name="AASHTO"/><ref name="23 CFR 603"/><ref name="23 CFR 625">{{cite web |title=Title 23 Code of Federal Regulations, Part 625.4 |url=https://www.law.cornell.edu/cfr/text/23/625.4 |publisher=U.S. Government Printing Office }}</ref><ref name="US MUTCD">{{cite book |title=Manual on Uniform Traffic Control Devices (MUTCD)|url=https://mutcd.fhwa.dot.gov/ |chapter=2009 Edition Chapter 2B. Regulatory Signs, Barricades, and Gates |chapter-url=http://mutcd.fhwa.dot.gov/htm/2009r1r2/part2/part2b.htm |publisher=Federal Highway Administration |quote=[Page 21] Sect.1A.13 —214. '''Speed'''—speed is defined based on the following classifications: (a) '''Average Speed'''—the summation of the instantaneous or spot-measured speeds at a specific location of vehicles divided by the number of vehicles observed. (b) '''Design Speed'''—a selected speed used to determine the various geometric design features of a roadway. (c) '''85th-Percentile Speed'''—the speed at or below which 85 percent of the motor vehicles travel. (d) '''Operating Speed'''—a speed at which a typical vehicle or the overall traffic operates. Operating speed might be defined with speed values such as the average, pace, or 85th-percentile speeds. (e) '''Pace'''—the 10 mph speed range representing the speeds of the largest percentage of vehicles in the traffic stream. [page 58] Section 2B.13 Speed Limit Sign (R2-1) Standard: 01 Speed zones (other than statutory speed limits) shall only be established on the basis of an engineering study that has been performed in accordance with traffic engineering practices. The engineering study shall include an analysis of the current speed distribution of free-flowing vehicles. ...12 '''When a speed limit within a speed zone is posted, it should be within 5 mph of the 85th-percentile speed of free-flowing traffic'''}}</ref><ref>{{cite web |title=National Committee on Uniform Traffic Control Devices (NCUTCD) |url=http://www.ncutcd.org/rulesroad042013.shtml |access-date=2016-02-26 |archive-url=https://web.archive.org/web/20160305153725/http://www.ncutcd.org/rulesroad042013.shtml |archive-date=2016-03-05 }}</ref> Functionality, this amounts to citizens "voting" a street's speed limit with their gas pedal from the influence of [[groupshift]]. As people generally follow explicit rules all the time of which they do not agree, it is often simply a jurisdiction's failure in their law to sufficiently quantify and disseminate fair notice of an explicit standard of care, such as the ACDA rule. Most DMV driver manuals teach the practice, but far fewer states explicitly back it up in their actual statutes and law enforcement.<ref name="CDLM"/><ref name="CA Handbook"/><ref name="AK Handbook"/><ref name="NC Handbook"/> If drivers were mindful of the ACDA, the ''operating speed'' would by definition not exceed the ''inferred design speed''.<ref name="AASHTO"/><ref name="US MUTCD"/> In some cases, police focused on driving while "influenced", pull over slower [[quartile]] sober night-time drivers moving no faster than they can stop within the radius of their headlights;<ref name="CDLM"/> this discourages adjusting speed downward from anything but the posted "maximum speed" permitted by law—which is determined as previously described. It is often unsafe or illegal to drive in excess of 40–50&nbsp;mph at night.<ref name="AAA headlights"/><ref name="NHTSA Night&Day"/><ref name="236 Cal. App. 2d 555"/><ref name="MTSpeedLaw">{{cite web |title=61-8-303(1)(b)&(3) - Speed restrictions |url=https://leg.mt.gov/bills/mca/title_0610/chapter_0080/part_0030/section_0030/0610-0080-0030-0030.html |website=Montana Code Annotated |publisher=[[State of Montana]] |access-date=4 July 2018 |quote=the speed limit for vehicles traveling...on any other public highway of this state is 70 miles an hour during the '''daytime''' and 65 miles an hour during the '''nighttime'''...Subject to the maximum speed limits set forth [above] a person shall operate a vehicle in a careful and prudent manner and at a reduced rate of speed no greater than is reasonable and prudent under the conditions existing at the point of operation, taking into account the amount and character of traffic, '''visibility''', weather, and roadway conditions.}}</ref><ref name="Leibowitz&Herschel"/><ref name="245 Mich. 88"/>

=="Assurance" beyond proximate edge of clear visibility as transference of liability==
A general principle in [[Legal liability|liability]] doctrine is than an accident which would not have occurred except for the action or inaction of some person or entity contrary to a [[legal duty|duty]] such as the exercise of [[ordinary care|proper care]] was the result of [[negligence]]. The liability [[Sample space|space]] from which one can recover<ref>{{cite web |url=http://www.leginfo.ca.gov/cgi-bin/displaycode?section=civ&group=03001-04000&file=3333-3343.7 |title=CA Civil Code §3333 |publisher=The State of California |quote=For the breach of an obligation not arising from contract, the measure of damages, except where otherwise expressly provided by this Code, is the amount which will compensate for all the detriment proximately caused thereby, whether it could have been anticipated or not. |access-date=2015-12-15 |archive-url=https://web.archive.org/web/20160115055251/http://www.leginfo.ca.gov/cgi-bin/displaycode?section=civ&group=03001-04000&file=3333-3343.7 |archive-date=2016-01-15 }}</ref> is typically, themselves, other parties, or nobody.<ref>{{cite court
|litigants=Cordova v. Ford, 46 Cal. App. 2d 180
|vol=46
|reporter=California Appellate Reports, Second Series
|opinion=180
|court=[[California courts of appeal|California Appellate Court]]
|date=7 November 1966
|url=http://law.justia.com/cases/california/calapp2d/246/180.html
|access-date=27 July 2013
|quote="All courts are agreed that the mere fact of a collision of two automobiles gives rise to no inference of negligence against either driver in an action brought by the other. ...When a vehicle operated by '''A''' collides with a vehicle operated by '''B''', there are four possibilities. '''A''' alone was negligent; '''B''' alone was negligent; '''both''' were negligent; or '''neither.''' Of these four only the first will result in liability of '''A''' to '''B'''. The bare fact of a collision affords no basis on which to conclude that it is the preponderant probability. '''The odds are against it.'''"
}} See [http://courts.ca.gov/opinions-slip.htm Official Reports Opinions Online]</ref> Jurisdictional exceptions permitting one to legally take "assurance" that the distance will be clear beyond the proximate edge of clear visibility and choose such a speed accordingly, transfers classic common law liability from that driver for his or her "blind" actions. This duty to assure clear distance ahead is inevitably transferred, as an [[externality]] to everybody or thing else who must instead warn the driver, such as the government, its road engineers, and maintainers.<ref name="22 Cal.2d 111">{{cite court |litigants=Peri v. L. A. Junction Railway, 22 Cal.2d 111 |vol=22 |reporter=Official California Reports, Second Series |opinion=111 |court=[[Supreme Court of California]] |publisher=Bancroft-Whitney; LexisNexis |date=3 May 1943 |url=http://scocal.stanford.edu/opinion/peri-v-l-junction-railway-25708 |quote=Today it is a matter of common knowledge that automobiles are driven at night on our great, wide, straight highways at speeds which do not allow adequate time or space in which to stop for unusual objects such as freight trains completely obstructing the highway unless some warning of the possible or probable presence thereof is given, especially where, as in the case of such trains, the bodies of the cars are apt to be above the direct beams of the automobile lights which the law requires to be projected below 42 inches at 75 feet from the vehicle. Recognizing this, our counties and state highway department place conspicuous warnings of all variations from the normal road. Drivers of ordinary prudence have grown to rely on the presence of such warnings. See [http://courts.ca.gov/opinions-slip.htm Official Reports Opinions Online]}}</ref><ref name="Kenworthy"/><ref name="38 Cal.App.4th 1187">{{cite court |litigants=Chowdhury v. City of Los Angeles, 38 Cal.App.4th 1187 |vol=38 |reporter=Official California Appellate Reports, 4th Series |opinion=1187 |court=[[California courts of appeal|California Appellate Court]] |publisher=Bancroft-Whitney; LexisNexis |date=September 5, 1995 |url=http://law.justia.com/cases/california/court-of-appeal/4th/38/1187.html |access-date=February 2016 |quote="A public entity does not create a dangerous condition on its property 'merely because of the failure to provide regulatory traffic control signals, stop signs, yield right-of-way signs, or speed restriction signs . . . .' (§ 830.4.) If, on the other hand, the government installs traffic signals and invites the public to justifiably rely on them, liability will attach if the signals malfunction, confusing or misleading motorists, and causing an accident to occur. See [http://courts.ca.gov/opinions-slip.htm Official Reports Opinions Online]}}</ref>

As it is generally probable and [[Proximate cause#Foreseeability|foreseeable]] that, chance will permit, and at some point there will be an obstruction beyond some driver's line of sight, such an entitlement challenges centuries<ref name="common law2"/><ref name="common law"/> of [[precedent]] in negligence doctrine in addition to posing difficult policy and engineering challenges. It also violates the [[calculus of negligence]]<ref name="Hand rule"/> because speed is an inherent factor in vehicular accidents which are a leading cause of priceless life loss<ref name="Traffic Safety Facts">{{cite web |url=http://www-nrd.nhtsa.dot.gov/Pubs/812169.pdf |title=Overview: 2013 data. (Traffic Safety Facts. Report No. DOT HS 812 169) |author=National Center for Statistics and Analysis |publisher=National Highway Traffic Safety Administration |location=Washington, DC |date=July 2015 |quote='''motor vehicle crashes in 2013 were the leading cause of death''' for children age 4 and every age from 16 to 24. ... In 2013, there were '''32,719 people killed''' in the estimated 5,687,000 police-reported motor vehicle traffic crashes; an estimated '''2,313,000 people were injured'''; and an estimated 4,066,000 crashes resulted in property damage only. An average of 90 people died each day in motor vehicle crashes in 2013, '''one fatality every 16 minutes'''. ... The estimated economic cost of all motor vehicle traffic crashes in the United States in 2010 (the most recent year for which cost data is available) was $242 billion. ... When quality of life valuations are considered, '''the total value of societal harm from motor vehicle crashes in the United States in 2010 was an estimated $836 billion.''' ... Speeding is one of the most prevalent factors contributing to traffic crashes.}}</ref><ref name="Harvard"/><ref name="Heinrich's Law">{{cite book |author=Herbert William Heinrich |title=Industrial accident prevention: a scientific approach |publisher=[[McGraw-Hill]] |year=1931 |lccn=31004075 |oclc=571338960 |url=http://catalog.hathitrust.org/Record/001106744 |quote=for every accident that causes a major injury, there are 29 accidents that cause minor injuries and 300 accidents that cause no injuries|series=McGraw-Hill insurance series |author-link=Herbert William Heinrich }}</ref><ref name="NYT">{{cite news |url=https://www.nytimes.com/2011/02/17/business/economy/17regulation.html |title=As U.S. Agencies Put More Value on a Life, Businesses Fret |author=Binyamin Appelbaum |date=February 16, 2011 |newspaper=[[The New York Times]] |quote=The Environmental Protection Agency set the value of a life at $9.1 million...}}</ref><ref name="cost-benefit">{{cite web |url=http://www.theglobalist.com/the-cost-of-a-human-life-statistically-speaking/ |title=The Cost of a Human Life, Statistically Speaking |author=Frank Partnoy |date=July 21, 2012 |website=The Globalist |quote=when the U.S. government permitted states to raise the speed limit from 55 to 65 miles per hour, many states did so, and drivers saved time by driving about two miles per hour faster on average. However, fatality rates rose by about one-third. Overall, people in the United States saved about 125,000 hours of driving [or about $1.5 million] per lost life. ... researchers have reached a consensus that $1.5 million is much too low [to trade-off for a life]. ... The Environmental Protection Agency set the value of a human life at $9.1 million. Meanwhile, the Food and Drug Administration put it at $7.9 million...}}</ref><ref name="Human Factors"/> and lawsuits, and the burden of a precautions speed is radically lower than the former.<ref name="cost-benefit"/>

The [[assumption of risk]] resulting from the unsafe activity of driving faster than one can stop within one's vision, does not depend ''ex post facto'' on what you happened to hit, for which by nature you could not have known; it could have been a moose or a luxury car. Furthermore, modern times still provide no [[legal remedies]] for [[Darwin Awards|Darwinian misfortune]] upon the entire class of unwarnable accidents where drivers and their passengers would not have collided into the likes of a moose,<ref name="deer"/> livestock,<ref name="CVC 21759"/> fallen tree, rock, jetsam, horse-drawn vehicle,<ref name="CVC 21759"/> stalled vehicle,<ref name="183 So. 2d 68">{{cite court |litigants=Self v. State Farm Mutual Automobile Insurance Co., 183 So. 2d 68 |vol=183 |reporter=So.2d |opinion=68 |court=Court of Appeal of Louisiana, Third Circuit |date=February 15, 1966 |url=https://scholar.google.com/scholar_case?case=10471683945633679546 |quote=The law imposes upon a following motorist a duty to exercise great care, sometimes referred to as extraordinary care. ... As a rule, when a following vehicle collides with the rear of the lead car, the following driver is considered to be at fault.}}</ref> school bus, garbage truck, mail carrier, snowplow, washout, snow drift, or slid off the road, were it not for their decisions to drive faster than dictated by the assured clear distance ahead. Regardless of what behavior an authority might encourage by fabricating new rights, it remains timeless that constituents cannot sue the wind for causing a wreck when it inevitably violates a "modern right to drive faster than permitted by the ACDA" by failing to warn them it knocked down a tree in a forest with many trees which all eventually fell. In this specific regard, jurisdictions which grant drivers the [[liberty]] to be fools from their own folly, are also condoning the [[collateral damage]] and life loss which is expected to occur. Moreover, modern life-entrusting consumers of [[taxi|driving services]] and [[driverless cars]]<ref name=":0">{{Cite journal|last1=Le Vine|first1=Scott|last2=Liu|first2=Xiaobo|last3=Zheng|first3=Fangfang|last4=Polak|first4=John|date=2016-01-01|title=Automated cars: Queue discharge at signalized intersections with 'Assured-Clear-Distance-Ahead' driving strategies|journal=Transportation Research Part C: Emerging Technologies|volume=62|pages=35–54|doi=10.1016/j.trc.2015.11.005|bibcode=2016TRPC...62...35L }}</ref> who suffer such caused injury are left without legal remedy for foreseeable outcome of imprudent speed; this in-turn unnecessarily transfers a substantive portion of the ACDA liability [[Sample space|space]] into [[act of god]], [[Federal Tort Claims Act|government claims]], [[strict liability]], or other [[verdict|findings]] from [[legal fiction]] which the justice system generally abhors. What modern times are changing is that one may assure the distance is clear ahead virtually through the [[Internet of Things]], as smart cars connect to get information from smart highways or pass what they see ahead or measure to traffic behind.<ref>{{cite web |url=http://www.its.dot.gov/landing/cv_pilots.htm |title=Connected Vehicle Pilot Program |publisher=US Department of Transportation |quote=The U.S. DOT connected vehicle research program is a multimodal initiative that aims to enable safe, interoperable networked wireless communications among vehicles, infrastructure, and personal communications devices.}}</ref> A fundamental corollary of the ACDA rule is that technology, expectations, and desires may modernize, but the laws of physics can not and do not.<ref name="Nixon">{{cite journal |author=Richard M. Nixon |title=Changing Rules of Liability in Automobile Accident Litigation |journal=Law and Contemporary Problems |volume=3 |pages=476–490 |number=4 |date=October 1936 |issn=1945-2322 |url=http://scholarship.law.duke.edu/lcp/vol3/iss4/3 |quote=The courts before and since that time, almost without exception, have insisted that the rules of law applicable to automobile cases, were no different from those which had been developed in the days of the horse and buggy. |doi=10.2307/1189341|jstor=1189341 |author-link=Richard M. Nixon }}</ref><ref name="175 Cal. 497">{{cite court |litigants=Cook v. Miller, 175 Cal. 497 |vol=175 |reporter=Official California Reports |opinion=497 |court=[[Supreme Court of California]] |publisher=Bancroft-Whitney; LexisNexis |date=June 19, 1917 |url=http://www.lexisnexis.com/clients/CACourts/ |quote=The cause of plaintiff having no time to avoid the collision was not the speed of the automobile, for it had come practically to a stop at the instant of the collision. It was his own speed that shortened his time. ... '''A horse''' can travel at the rate of fifteen miles an hour, and even faster, for a short time. But in the days of exclusively '''horse-drawn vehicles''' one who crossed a street at such a place going at fifteen miles an hour would have been considered reckless. There have been city ordinances forbidding a team from crossing a street intersection faster than a walk. ( Stein v. United Railroads, 159 Cal. 371, [113 Pac. 663].) '''Since our eyes have become somewhat accustomed to greater speed, the recklessness of fifteen miles an hour may not seem so obvious, but the danger is the same'''. ... A speed which carries a person twenty-two feet in one second of time at a "blind corner," with standing auto trucks projecting twelve feet into the street, obstructing the vision of the intersecting street until the last truck is reached, and with a wagon ahead of him, is not that speed which a person exercising ordinary prudence would choose at such a place, out of due regard for his own safety or that of others. '''Such speed may not be unusual at the present time, even under similar circumstances. But the person who receives an injury from a collision, while going at that rate under the conditions here existing, should not expect the other person to pay him the damages caused thereby.'''}}</ref> The deceleration coefficients and reactions times may change from conveyance by [[chariot]], [[horse and buggy]], [[internal combustion engine]], [[electric motor]], and by driverless car, but the equations governing stopping distances are immutable. Finally, where it is the policy of the law not to fault well intending diligent citizens for innocent mistakes,<ref name="83 Cal. App. 2d 377"/><ref name="43 Cal.2d 626">{{cite court |litigants=Nevis v. Pacific Gas & Electric Co., 43 Cal.2d 626 |vol=43 |reporter=Official California Reports, Second Series |opinion=626 |court=[[Supreme Court of California]] |date=November 9, 1954 |publisher=Bancroft-Whitney; LexisNexis |url=http://scocal.stanford.edu/opinion/nevis-v-pacific-gas-electric-co-29632 |quote=Nonnegligent ignorance of the facts which bring a regulation into operation will support a finding that violation thereof is civilly excusable. [http://www.lexisnexis.com/clients/CACourts/ See Official Reports Online]}}</ref> human life reaps continued benefit from the ACDA duty of which instills the necessary room to survive uninjured from such [[Absolute probability judgement|foreseeable and excusable error]] while adding [[Redundancy (engineering)|redundancy]] in the responsibility to avoid a collision; mere unilateral duties laid down to assure the safety of others tend to result in hazardous [[risk compensation]] by those unfettered parties<ref>{{cite journal |jstor=1830396 |title=The Effects of Automobile Safety Regulation |author=Sam Peltzman |journal=Journal of Political Economy |volume=83 |number=4 |pages=677–726 |date=August 1975 |doi=10.1086/260352|s2cid=153473566 }}</ref> resulting in a [[moral hazard]].

Allowing one to drive faster than their vision permits them to safely stop, results in there being no core [[standard of care]] regarding safe speed making unsafe speed laws [[void for vagueness]].<ref name="1998 MT 321"/> The ACDA minimum standard gives fair notice of what conduct is prohibited, and people of ordinary intelligence can apply their braking experience or the [[Assured Clear Distance Ahead#Seconds of distance to stop rule|seconds of distance to stop rule]] to the distance they can see;<ref name="Gibson&Crooks"/> once one is allowed to cruise-on without control beyond the edge of visibility, there is little consensus on what arbitrary speed is unsafe, or what to assume of the vague conditions there-past.<ref name="void for vagueness">{{cite news |url=https://www.nytimes.com/1998/12/25/us/montana-s-speed-limit-of-mph-is-overturned-as-too-vague.html |title=Montana's Speed Limit of ?? M.P.H. Is Overturned as Too Vague |author=Jim Robbins |date=December 25, 1998 |work=[[The New York Times]] |quote= The challenge to the speed limit was brought by Rudy Stanko, a cattle buyer in Billings who had contested three tickets. "I asked a cop how fast I could go and he never gave me an answer," Mr. Stanko said today. "They said it's up to the discretion of the cop and that ain't right. Let us decide how fast we want to travel." Although the court threw out a speeding ticket Mr. Stanko had received for traveling 102 miles an hour, it upheld two reckless driving counts -- one for traveling 117 m.p.h., the other for 121 m.p.h. Both violations were on two-lane highways as he crested a hill.}}</ref>

To be able to guarantee "assurance" beyond proximate edge of clear visibility, in doing so exempting ACDA duty, a road must be designed and maintained such that there is not a chance of obstruction in one's lane beyond the proximate edge of clear visibility. A road's vertical [[Geometric design of roads#Profile|profile]] must be assured to have such a curvature as not to hide hazards close behind its crests. [[Discretion]] for drivers and pedestrians to enter onto a potentially occupied lane from a side street must be assuredly eliminated such as with fences, merge lanes, or signalized access. There must also be an assurance of no opportunity for animals and debris to enter from side lots, and that there are continuous multi-hourly maintenance [[highway patrol|patrols]] performed. Furthermore, such road sections must be distinguished from other roads so that the driver could clearly and immediately know when he or she may or may not take such extended "assurance". Few roads might meet these requirements except some of the highest functional classification [[controlled-access highways]] such as [[freeways]] and [[autobahn]]s.<ref name="FHWA"/>

Even if such criteria are met, the law must also exempt driver liability for maintaining clear distance ahead. In most democracies, such liability for failures of the distance to remain clear beyond line of sight would ultimately be transferred to its taxpayers.<ref name="Kenworthy"/> This only generally occurs when governments have been tasked by constituents or their courts to take the responsibly to design and maintain roadways that "assure" the distance will be clear beyond the proximate edge of clear visibility. Pressures to make such changes may arise from cultural [[Wikibooks:Professionalism/Diane Vaughan and the normalization of deviance|normalization of deviance]] and unnecessary risk, misunderstanding the purpose of the road [[functional classification]] system, underestimation of increased risk, and reclamation of commute time.<ref name="FHWA"/>

One of the greatest difficulties created by such an extension of the ACDA is the frequency at which roads reduce their [[functional classification]]<ref name="FHWA"/> unbeknownst to drivers who continue unaware they have lost this extended "assurance" or do not understand the difference. Such nuance in applicable jurisdictions is a prolific source of accidents.<ref name="106 Cal. App. 2d 294"/> In the [[United States]], there is no explicit road marking promising clear distance beyond line of sight in the [[Manual on Uniform Traffic Control Devices]], although there are [[Road signs in the United States#W19 Series: End of Controlled Access Highway|signs]] communicating "[https://web.archive.org/web/20160915123237/http://www.trafficsigns.com/w14-4-limited-sight-distance-sign.html limited sight distance]", "[https://mutcd.fhwa.dot.gov/htm/2009r1r2/part2/part2c.htm#section2C18 hill blocks view]", "[https://mutcd.fhwa.dot.gov/htm/2009r1r2/part2/part2c.htm#section2C46 crossroad ahead]", and "[https://mutcd.fhwa.dot.gov/htm/2009r1r2/part2/part2c.htm#section2C24 freeway ends]".<ref name="MUTCD">{{cite book |url=https://mutcd.fhwa.dot.gov/pdfs/2009r1r2/pdf_index.htm |title=Manual on Uniform Traffic Control Devices for Streets and Highways |publisher=US Dept. of Transportation, Federal Highway Administration |edition=2009 |year=2012 |pages=117, 119, 127 |isbn=978-1598045369 |quote=The use of warning signs should be kept to a minimum as the unnecessary use of warning signs tends to breed disrespect for all signs.(2C.02.02)...Vehicular Traffic Warning signs should be used only at locations where the road user's sight distance is restricted, or the condition, activity, or entering traffic would be unexpected.(2C.49.03)}}</ref> A partial solution to this challenge is to remove driver discretion in determining whether the ACDA is extended beyond line of sight, by explicitly designating this law change to certain marked high functional classification roadways having meet strict engineering criteria.<ref name="FHWA"/>

The ACDA rule is analogous to aviation [[visual flight rules]], and its discussed exception—allowed only in a well regulated control zone—is analogous to [[instrument flight rules]]. Unlike both visual and instrumental flight rules, where federal and international [[administrative law]] applies seamlessly and uniformly across the states, the ACDA rule governing ground transportation is relatively variegated across states and [[Circuit court|judicial circuits]].<ref name="1998 MT 321">{{cite court |litigants=State of Montana, v. Rudy Stanko |vol=1998 |reporter=MT |opinion=321 |pinpoint=HN 30 |court=[[Supreme Court of Montana]] |date=23 December 1998 |url=https://caselaw.findlaw.com/mt-supreme-court/1110919.html |access-date=February 2016 |quote=...we conclude that that part of § 61-8-303(1), MCA, which makes it a criminal offense to operate a motor vehicle "at a rate of speed ․ greater than is reasonable and proper under the conditions existing at the point of operation" is void for vagueness on its face and in violation of the Due Process Clause of Article II, Section 17, of the Montana Constitution.}}</ref><ref name="74 A.D.2d 806"/><ref name="red-blue">{{cite web |url=http://www.fairwarning.org/2012/11/traffic-deaths-a-surprising-dimension-of-the-red-state-blue-state-divide/ |title=Traffic Deaths: A Surprising Dimension of the Red State-Blue State Divide |author=Stuart Silverstein |date=November 20, 2012 |publisher=FairWarning |quote=blue states tend to adopt stronger safety laws, while red states opt for looser regulation}}</ref><ref name="State traffic data">{{cite web |url=http://www-nrd.nhtsa.dot.gov/Pubs/812196.pdf |title=State traffic data: 2013 data (Traffic Safety Facts. Report No. DOT HS 812 196) |author=National Center for Statistics and Analysis |publisher=National Highway Traffic Safety Administration |location=Washington, DC |date=September 2015 |quote=Montana had the highest fatality rate per 100 million VMT (1.90) in the United States, while Massachusetts and the District of Columbia had the lowest (0.58 and 0.57) in 2013.}}</ref><ref>{{cite web |url=http://www.iihs.org/iihs/topics/t/general-statistics/fatalityfacts/state-by-state-overview |title=General statistics |publisher=Insurance Institute for Highway Safety (IIHS) |quote=The fatality rate per 100,000 people ranged from a low of 3.1 in the District of Columbia to a high of 22.6 in Montana. The death rates per 100 million vehicle miles traveled ranged from 0.56 in the District of Columbia to 1.96 in Montana.}}</ref> Primitive patchwork governance over a prominent [[Commerce Clause|interstate commercial subject]], in a modern era where citizens quickly and more frequently travel father than ever before, creates problems for modern driverless cars which are programmed, distributed, sold, and traded at national levels.<ref name=":0" /><ref name="uniform">{{cite journal |author=R. J. H. |title=The Uniform Motor Vehicle Act in Virginia |journal=Virginia Law Review |volume=23 |number=3 |pages=351–358 |date=January 1937 |doi=10.2307/1067282 |jstor=1067282 |quote=The attempt of this conference was to reduce road accidents among the states, and to this end an exhaustive study of road conditions and accidents was made. The need for such uniformity is obvious when we consider that the late 1920s the major part of the traffic regulation was by municipalities; it had mainly been enacted ten to fifteen years before and hence left out of account the vast increase in number, speed, and use of automobiles. Each town and city had a different set of rules, confusing the motorist on tour. This dangerous chaos has been largely obviated by the substantial enactment in most states of the Uniform Act...}}</ref><ref name="rules"/> As opposed to a strict standard of care,<ref name="121 Cal. 227">{{cite court |litigants=Herbert v. Southern Pac. Co., 121 Cal. 227 |vol=121 |reporter=Official California Reports |opinion=227 |court=[[Supreme Court of California]] |publisher=Bancroft-Whitney; LexisNexis |date=June 20, 1898 |url=http://www.lexisnexis.com/clients/CACourts/ |quote=the cases arising from injuries suffered at railroad crossings have been so numerous, and upon certain points there has been such absolute accord, that what will constitute ordinary care in such a case had been precisely defined, and, if any element is wanting, the courts will hold as matter of law that the plaintiff has been guilty of negligence. And, when injury results which might have been avoided by the use of proper care, ... the amount of care, as well as the nature of it, has been settled.}}</ref><ref name="275 U.S. 66"/><ref name="Holmes"/><ref name="SCOTUK">{{cite court |litigants=Healthcare at Home Limited v. The Common Services Agency, [2014] UKSC 49 |court=[[Supreme Court of the United Kingdom]] |date=30 July 2014 |url=https://www.supremecourt.uk/decided-cases/docs/UKSC_2013_0108_Judgment.pdf |quote=It follows from the nature of the reasonable man, as a means of describing a standard applied by the court, that it would be misconceived for a party to seek to lead evidence from actual passengers [i.e. "the right-thinking member of society," "the [[officious bystander]]," "the reasonable parent," "the reasonable landlord," "the fair-minded and informed observer,"...] on the [[The man on the Clapham omnibus|Clapham omnibus]] as to how they would have acted in a given situation or what they would have foreseen, in order to establish how the reasonable man would have acted or what he would have foreseen. Even if the party offered to prove that his witnesses were reasonable men, the evidence would be beside the point. The behaviour of the reasonable man is not established by the evidence of witnesses, but by the application of a legal standard by the court. The court may require to be informed by evidence of circumstances which bear on its application of the standard of the reasonable man in any particular case; but it is then for the court to determine the outcome, in those circumstances, of applying that impersonal standard.}}</ref> delegation of such standard to a [[jury]]<ref>{{cite journal |url=https://www.repository.law.indiana.edu/facpub/749 |title=Issue on the Selection and Function of the Modern Jury: Article: Who is an Impartial Juror in an Age of Mass Media?, 40 Am. U.L. Rev. 631 |author1=Newton N. Minow |author2=Fred H. Cate |journal=American University Law Review |volume=40 |page=631 |date=Winter 1991 |quote=We have a criminal jury system which is superior to any other in the world; and its efficiency is only marred by the difficulty of finding twelve every day men who don't know anything and can't read. |access-date=2016-01-05 |archive-url=https://web.archive.org/web/20160131154541/https://litigation-essentials.lexisnexis.com/webcd/app?action=DocumentDisplay&crawlid=1&doctype=cite&docid=40+Am.+U.L.+Rev.+631&srctype=smi&srcid=3B15&key=ebbc7b30d51ec9526831d6620ff9a2ea |archive-date=2016-01-31 }}</ref> assumes the [[representativeness heuristic]]<ref name="law of small numbers">{{cite journal |title=Belief in the law of small numbers. |author1=Amos Tversky |author2-link=Daniel Kahneman |author2=Daniel Kahneman |journal=Psychological Bulletin |volume=76 |number=2 |pages=105–110|date=August 1971 |doi=10.1037/h0031322 |quote=people have erroneous intuitions about the laws of chance. In particular, they regard a sample randomly drawn from a population as highly representative, I.e., similar to the population in all essential characteristics.|citeseerx=10.1.1.592.3838 |s2cid=5883140 |author1-link=Amos Tversky }}</ref> for twelve people to determine ordinary care representative of everyone while ignoring its [[insensitivity to sample size]], which of course when applied to multiple cases involving identical situational circumstances results in many verdicts with opposing extreme views,<ref name="Holmes"/> which works against the utility of the law by making it arbitrarily [[vagueness doctrine|vague]].<ref name="275 U.S. 66">{{cite court |litigants=Baltimore & Ohio R. Co. v. Goodman, 275 U.S. 66 |vol=275 |reporter=[[United States Reports]] |opinion=66 |court=[[Supreme Court of the United States]] |date=October 31, 1927 |url=https://supreme.justia.com/cases/federal/us/275/66/case.html |quote=In an action for negligence, the question of due care is not left to the jury when resolved by a clear standard of conduct which should be laid down by the courts ... If, at the last moment, [he] found himself in an emergency, it was his own fault that he did not reduce his speed earlier or come to a stop.}}</ref><ref name="Holmes"/> A national uniformity standard which either administratively lays down the ACDA law as has been done for aircraft, or requires states to legislatively enact in order to receive federal DOT funding as has been done for the national legal drinking age, is a subject of debate for those who argue far more people die in cars than in aircraft.<ref name="Traffic Safety Facts"/><ref name="Harvard">{{cite web |url=http://journalistsresource.org/studies/environment/transportation/comparing-fatality-risks-united-states-transportation-across-modes-time |title=Transportation safety over time: Cars, planes, trains, walking, cycling |author=Leighton Walter Kille |publisher=Harvard Kennedy School's Shorenstein Center and the Carnegie-Knight Initiative |date=October 5, 2014 |quote=Since 1980 the average horsepower of U.S. cars more than doubled, and speed limits have risen significantly, greatly increasing the potential for damage, loss of life and injuries. ... "One might argue that transportation equipment, and in particular the motor vehicle, must be the most dangerous machines that we interact with on a daily basis," the researcher states. "The annual toll in motor vehicle crashes exceeds the deaths resulting from the next most dangerous mechanical device, firearms, by about 40%."}}</ref><ref name="Human Factors">{{cite book |chapter-url=http://www.nap.edu/read/4940/chapter/13#242 |title=Emerging Needs and Opportunities for Human Factors Research |chapter=9 |author1=Raymond S. Nickerson |author2=The National Research Council |publisher=The National Academies Press |date=September 15, 1995 |isbn=978-0309052764 |doi=10.17226/4940 |quote=In the United States, motor vehicle accidents are the leading cause of death for people between the ages of 1 and 38 and are responsible for more deaths than all other causes combined between the ages of 15 and 24 ... the difficulty of estimating distance and velocity is assumed to account for the frequency of accidents involving a vehicle turning left in the face of oncoming traffic. ... many laws require operators of vehicles to accomplish tasks that are not within their capabilities. This leads to unnecessary litigation and appellate reviews and creates a disrespect for laws. If statutes such as the Assured Clear Distance Ahead rule and regulations governing the use of alcohol were examined in relation to the behavioral sciences literature on human capabilities and limitations while operating a vehicle, the findings could lead to more rational laws and codes ... In stark contrast with automobile travel, commercial aviation is the safest form of mass transportation.}}</ref><ref>{{cite web |url=https://www.ntsb.gov/investigations/data/Pages/Data_Stats.aspx |title=US Civil Aviation Accident Statistics |publisher=National Transportation Safety Board }}</ref> While [[group polarization]] towards safety has shifted the criminal blood alcohol threshold below levels for which the risk is statistically marginal,<ref name="Kloeden et. al."/><ref>{{cite book |url=http://www.euro.who.int/en/publications/abstracts/preventing-road-traffic-injury-a-public-health-perspective-for-europe-2004 |title=Preventing road traffic injury: a public health perspective for Europe |author1=Francesca Racioppi |author2=Lars Eriksson |author3=Claes Tingvall |author4=Andres Villaveces |year=2004 |page=47 |publisher=World Health Organization |isbn=978-9289010931 |quote=See Figure 5.2 (Chapter 5, page 47)}}</ref> the tolerance for speeding—of which each speed unit increment carries an equatable risk relative to BAC<ref name="Kloeden et. al.">{{cite web |url=https://infrastructure.gov.au/roads/safety/publications/1997/pdf/Speed_Risk_1.pdf |title=Travelling Speed and the Risk of Crash Involvement |author1=C.N. Kloeden |author2=A.J. McLean |author3=V.M. Moore |author4=G. Ponte |volume=1 |page=54 |publisher=NHMRC Road Accident Research Unit, The University of Adelaide |quote=the relative risk of an injury crash when travelling at 65 km/h in a 60 km/h speed limit zone is similar to that associated with driving with a blood alcohol concentration of 0.05 g/100mL. By strange coincidence, if the blood alcohol concentration is multiplied by 100, and the resulting number is added to 60 km/h, the risk of involvement in a casualty crash associated with that travelling speed is almost the same as the risk associated with the blood alcohol concentration. Hence, the risk is similar for 0.05 and 65, as noted; for 0.08 and 68; for .12 and 72, and so on...}}</ref>—remains relatively neglected. Speed is responsible for more crashes and economic loss than is alcohol.<ref name="Traffic Safety Facts"/> The discrepancy may be partly explained by powerful [[special interest groups]] that are [[lobbying]] against drunk driving and for loser speed regulation.<ref>{{cite web |url=http://www.pe.com/articles/speed-776756-survey-limit.html |title=TEMECULA: Inquiries prompt new speed survey |author=Aaron Claverie |publisher=The Press Enterprise |date= August 13, 2015 |quote=the city took a look at the speed limit after Kelly, with support from the Automobile Club of Southern California, presented a detailed breakdown of why he feels the survey was incorrect.}}</ref>

==Derivations==
===Case 1: Safe speed as a function of forward line-of-sight===
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
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|title=Derivation of ACDA 1
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[[File:Free body.svg|thumb|Forces on a vehicle skidding down a grade of angle ''θ''.]]

Starting with [[Newton's laws of motion#Newton's second law|Newton's Second Law of Motion]] and the Laws of [[Friction]]:

:<math> F_\text{total} = F_\text{friction} + F_\text{gravity} \sin\theta </math>

:<math> F_\text{total} = \mu F_\text{normal} + m g \sin\theta </math>

:<math> F_\text{total} = \mu m g \cos{\theta} + m g \sin\theta </math>

Equating the net [[force]] to [[mass]] times [[acceleration]]:

:<math> F_\text{total}= m a </math>

:<math> \mu m g \cos\theta + m g \sin\theta = m a </math>

:<math> a = g(\mu \cos\theta + \sin\theta) </math>

Invoking the [[Equations of motion#Uniform acceleration|equations of motion]] and substituting acceleration:

:<math> d = \frac{v^2}{2 a} </math>
:<math> d = \frac{v^2}{ 2 g(\mu \cos\theta + \sin\theta)} </math>

[[Small-angle approximation]]:

:<math> \sin\theta \approx \theta </math>
:<math> \cos\theta \approx 1 - \frac {\theta^2}{2} </math>

Substituting the small angle approximations, and exploiting that the product of a small angle squared, in radians, with the friction coefficient, θ<sup>2</sup>μ, is insignificant (for a steep 20% slope and a good friction coef. of 0.8, this equals (.2)<sup>2</sup>x0.8≈0.03):

:<math> d \approx \frac{v^2}{ 2 g[\mu (1 - \frac {\theta^2}{2} ) + \theta]} \approx \frac{v^2}{ 2 g(\mu + \theta)}</math>

Now, the total stopping distance is the sum of the braking and perception-reaction distances:

:<math> d_\text{total} = d_\text{braking} + d_\text{perception-reaction} </math>

:<math> d_\text{total} \approx \frac{v^2}{ 2 g(\mu + \theta)} + v t_{pr} </math>

Isolating zero as preparation to solve for velocity:

:<math> \frac{1}{2 g (\mu + \theta)} v^2 + v t_{prt} - d_\text{total} \approx 0 </math>

[[Completing the square]] or invoking the [[quadratic formula]] to find the solution:

:<math> v \approx \sqrt{(\mu + \theta)^2 g^2 t_{prt}^2+ 2 (\mu + \theta) g d_\text{total} } - ( \mu + \theta ) g t_{prt} </math>

Use [[small-angle approximation]] to obtain a more field-able version of the above solution in terms of percent [[Grade (slope)|grade]]/100 "[[Cant (road/rail)|e]]" instead of an angle θ in radians:

:<math> \theta \approx \tan(\theta) = \frac{\%\text{grade}}{100} </math>

Substituting the angle as described produces the form of the formula of case 1 ():

:<math> V_{BSL1} \approx \sqrt{(\mu + e)^2 g^2 t_{prt}^2+ 2 (\mu + e) g d_{ACDA} } - (\mu+e) g t_{prt} </math>

The Basic Speed Law constrains the assured clear distance ahead to the total stopping distance, and the small angle value of [[Grade (slope)|road grades]] approximates the [[Cant (road/rail)|superelevation]] "e."

Many roadways are level, in which case the small angle approximations or superelevation may be dropped altogether:
:<math> V_{BSL1} = \sqrt{\mu^2 g^2 t_{prt}^2+ 2 \mu g d_{ACDA} } - \mu g t_{prt} </math>

''This model ignores the effects of [[air drag]], [[rolling resistance]], [[Lift (force)|lift]], and [[Theory of relativity|relativity]] as a vehicle's great [[momentum]] and [[weight]] dominate these factors; they increase the complexity of the formulas while insubstantially changing the outcomes in practically all driving situations except ultra-low-mass [[bicycles]] stopping from inherently dangerously high speeds; usability to the layman and conformance with current standard engineering assumptions<ref name="AASHTO"/><ref name="VA Table"/> is the objective and a vehicle's [http://hpwizard.com/aerodynamics.html lift factor] is often inaccessible. Learn a [[Horizontal plane|level]] ground model with most of those effects [http://hpwizard.com/braking.html#stopping-distance here] or read about the [[automobile drag coefficient]].''
{{hidden end}}

===Case 2: Safe speed as a function of horizontal line-of-sight===
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
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The time required for an obstruction with speed v<sub>i</sub> to transect the horizontal sight distance d<sub>i</sub>:

:<math> t = \frac{d_i}{v_i} </math>

The time required to travel down a road at speed v to said obstruction of distance d away:

:<math> t= \frac{d}{v} </math>

Equating the two times:

:<math> \frac{d}{v} = \frac{d_i}{v_i} </math>

Solving for this distance:
:<math> d=\frac{v d_{i}}{v_i} </math>

Equating this to the total stopping distance, which is the sum of braking and perception-reaction distances:
:<math> \frac{v d_{i}}{v_i} = \frac{v^2}{2 g (\mu + e)} + v t_{prt} </math>

Isolating zero, and factoring out a v:
:<math> v \left[ \frac{v}{2 g (\mu + e)} + \left(t_{prt} - \frac{ d_{i}}{v_i}\right) \right] = 0 </math>

Solving for the non-trivial case (or may distribute v in equation above and apply quadratic formula for same result):
:<math> \frac{v}{2 g (\mu + e)} + (t_{prt} - \frac{ d_i}{v_i}) = 0 </math>

The solution to the above equation, which provides the maximum safe speed as a function of horizontal sight distance, intercept velocity, and road-tire friction coefficient:
:<math> v = 2 g (\mu + e) ( \frac{ d_{i}}{v_i} - t_{prt}) </math>

{{hidden end}}

===Case 3: Safe speed as a function of intersectional setback===
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
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The time required for a vehicle to enter a controlled intersection from a stop is the sum of the perception time (t<sub>p</sub>), the time required to actuate an automatic transmission or shift to first gear (t<sub>c</sub>), and the time to accelerate and enter or traverse the road (t<sub>a</sub>). The sum of the first two quantities is t<sub>pc</sub>.

:<math> t= t_p + t_c + t_a = t_{pc} + t_a </math>

The time required for a vehicle entering with acceleration a<sub>i</sub> to transect the sum of the setback and shoulder distances d<sub>i</sub> under uniform acceleration a<sub>i</sub> from a stop via the [[Equations of motion#Constant linear acceleration: collinear vectors|equations of motion]]:

:<math> t_a =\sqrt{ \frac{ 2 d_i }{a_i} } </math>

The time required to travel down a road at speed v to said obstruction of distance d away:

:<math> t= \frac{d}{v} </math>

Equating the two times:

:<math> \frac{d}{v} =\sqrt{ \frac{ 2 d_i }{a_i} } + t_{pc} </math>

Solving for this distance:
:<math> d = v \left( \sqrt{ \frac{ 2 d_i }{a_i} } + t_{pc} \right) </math>

Equating this to the total stopping distance, which is the sum of braking and perception-reaction distances:
:<math> v \left( \sqrt{ \frac{ 2 d_i }{a_i} } + t_{pc} \right) = \frac{v^2}{2 g (\mu + e)} + v t_{prt} </math>

Isolating zero, and factoring out a v:
:<math> v [ \frac{v}{2 g (\mu + e)} + \left( t_{prt} - \sqrt{ \frac{ 2 d_i }{a_i} } - t_{pc} \right) ] = 0 </math>

Solving for the non-trivial case (or may distribute v in equation above and apply quadratic formula for same result):
:<math> \frac{v}{2 g (\mu + e)} + \left( t_{prt} - \sqrt{ \frac{ 2 d_i }{a_i} } - t_{pc} \right) = 0 </math>

The solution to the above equation, which provides the maximum safe speed as a function of horizontal setback, intercept acceleration, and road-tire friction coefficient:
:<math> v = 2 g (\mu + e) \left( \sqrt{ \frac{ 2 d_i }{a_i} } + t_{pc} - t_{prt} \right) </math>

{{hidden end}}

===Case 4: Safe speed as a function of following distance===
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From the [[Equations of motion#Constant linear acceleration: collinear vectors|equations of motion]]:

:<math> t_g = \frac{d}{v} </math>

Isolating for speed:

:<math> v = \frac{d}{t_g} </math>

{{hidden end}}

===Case 5: Safe speed as a function of critical speed===
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
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[[File:Free body.svg|thumb|Forces on a vehicle skidding down a grade of angle ''θ''.]]

Starting with [[Newton's laws of motion#Newton's second law|Newton's Laws of Motion]], the Laws of [[Friction]], and [[Centripetal force#Formulae|Centripetal force]]:

:<math> F_\text{centripetal} \cos{ \theta } = F_\text{friction} + F_\text{gravity} \sin\theta </math>

Substituting formulas for [[Centripetal force#Formulae|Centripetal force]], frictional force, and gravitational force:

:<math> m \frac{v^2}{r} \cos\theta = \mu F_\text{normal} + m g \sin\theta </math>

The normal force is equal and opposite to the sum of the gravitational and centripetal components:

:<math> m \frac{v^2}{r} \cos\theta = \mu (m g \cos{\theta} + m \frac{v^2}{r} \sin\theta ) + m g \sin\theta </math>

Isolate <math>v</math> terms:

:<math> \frac{v^2}{r} \cos\theta - \mu \frac{v^2}{r} \sin\theta = g (\mu \cos\theta + \sin\theta ) </math>

Then solve for <math>v</math>:

:<math> v^2 ( \cos\theta - \mu \sin\theta ) = g r (\mu \cos\theta + \sin\theta) </math>

To obtain:
:<math> v = \sqrt { \frac{g r (\mu \cos\theta + \sin\theta) } { \cos\theta - \mu \sin\theta } } </math>
This is the full solution, however most corners are banked at less than 15 degrees (≈28% grade), so in such conditions, a fieldable small angle approximation may be used.

Substituting [[small-angle approximation]]s sin&nbsp;''θ''&nbsp;≈&nbsp;''θ'', cos&nbsp;≈&nbsp;1&nbsp;−&nbsp;''θ''<sup>2</sup>/2:

:<math> v \approx \sqrt { \frac{g r [\mu (1- \frac {\theta^2} {2}) + \theta ] } { 1- \frac {\theta^2}{2} - \mu \theta } } </math>

Exploit that a small angle squared, in radians, is insignificant by substituting θ<sup>2</sup>≈0 which obtains the formula used in case 5 (also tan&nbsp;θ≈e):

:<math> v \approx \sqrt { \frac{g r (\mu + \theta ) } { 1 - \mu \theta } } \approx \sqrt { \frac{g r (\mu + e ) } { 1 - \mu e } } </math>

{{hidden end}}

===Seconds of distance to stop rule===
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
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The ''seconds-of-distance-to-stop rule'' is derived as follows.

We first obtain the total stopping distance and then convert it into travel time, which is more easily applicable by the driver.

:<math> d_\text{total} = d_\text{braking} + d_\text{perception-reaction} </math>

Invoking the [[Equations of motion#Uniform acceleration|equations of motion]],

:<math>d_\text{braking} = \frac{v^2}{2 a}</math>

:<math>d_\text{total} = \frac{v^2}{2 a} + v t_\text{prt}</math>

where

:<math>a=\mu g</math>.

The time it takes to casually traverse the stopping distance at the travel speed is

:<math>t=\frac{d_\text{total}}{v}</math>.

Substituting the former into the latter,

:<math>t=\frac{v}{2 \mu g}+t_\text{prt}</math>.

This can be simplified into the rule-of-thumb form

:<math>t=C \cdot v + t_\text{prt}</math>

by noting that

:<math>C=\frac{f}{2 \mu g}</math>.

Substituting (US Customary units)

:<math>\mu \approx \tfrac{7}{10}</math> (dry) or <math>\tfrac{5}{10}</math> (wet) or <math>\lessapprox \tfrac{2}{10}</math> (snow); <math>g \approx 32\;{\rm ft}\;{\rm s}^{-2} </math>, <math>f=\tfrac{22\;{\rm ft}\;{\rm s}^{-1}}{15\;{\rm mi\;h^{-1}}}</math> (convert mph to fps); <math>t_{prt}=1.5\;{\rm s},</math>

we have

:<math>C=\tfrac{1}{30}</math> (dry), <math> \tfrac{1}{20}</math> (wet), and <math> \tfrac{1}{10}</math> (snow).

This results in a seconds-of-distance-to-stop rule (in MPH) of

:<math>t=\frac{v}{30} + 1.5</math> (dry pavement)

:<math>t=\frac{v}{20} + 1.5</math> (wet pavement)

:<math>t=\frac{v}{10} + 1.5</math> (snow, hard-packed).

The dry rule does allow one to travel faster in dry weather, but expect emergency deceleration to be a bit uncomfortable. If one desires to remember only one rule, use the wet one. However, because the difference between wet and dry is half-a-second at 30 MPH and one second at 60 MPH, and because dividing by two is easier than three, we can use a correctable rule of thumb:

:::<math>\color{Sepia}{t\approx\frac{v}{20} + 1 \quad \text{(general rule of thumb)}}</math> ''(instead add 2+ in wet or complex conditions, and also instead divide by 10 in snow/ice)''

For example, a speed of {{convert|60|mph}} corresponds to stopping distance of 4 seconds' travel at 60&nbsp;mph. Drivers that require additional perception-reaction time, such as novices, elderly, or those in complex or adverse environments, can benefit by adding additional seconds.<ref>{{cite journal |title=Effects of uncertainty, transmission type, driver age and gender on brake reaction and movement time. |author1=Lora Warshawsky-Livne |author2=David Shinar |journal=Journal of Safety Research |volume=33 |issue=1 |date=Spring 2000 |pages=117–128 |issn=0022-4375 |doi=10.1016/S0022-4375(02)00006-3 |pmid=11979633 |quote=Perception-reaction time increased significantly from 0.32 to 0.42 s (P<.05) as uncertainty increased but brake-movement time did not change. Perception-reaction time increased (from 0.35 to 0.43 s) with age but brake-movement time did not change with age. Gender did not affect perception-reaction time but did affect brake-movement time (males 0.19 s vs. females 0.16 s).}}</ref><ref>{{cite journal |title=On the speed of mental processes. |author=FC Donders |journal=Acta Psychologica |volume=30 |pages=412–31 |date=January 1969 |doi=10.1016/0001-6918(69)90065-1 |pmid=5811531 |issn=0001-6918 |oclc=1447968 }}</ref>

The time to traverse your stopping distance at travel speed should not be confused with the braking time to come to a full stop, which is a number nearly twice this value ( {{math| <var>t</var>{{=}}{{sfrac|<var>v</var>|<VAR>&mu;</VAR> g}}+t<sub>ptr</sub>}} ). As one is continually slowing down while braking, it will naturally take longer to get to the stopping limit.

A more correct perception-reaction time of one-and-a-half seconds is commonly used by the mathematically inclined.<ref name="VA Table"/><ref name="Olsen&Sivak"/> Doing so to obtain your "seconds-of-distance-to-stop" for ''dry pavement'' and then converting time to actual distance by multiplying it by the travel velocity and {{math|{{sfrac|22|15}}}} to convert MPH to fps will yield results in close agreement with [http://law.lis.virginia.gov/vacode/46.2-880/ this table].

Whereas most driving is done below {{convert|80|mph}}, ''maintaining a blanket 5 or 6 seconds of travel time to the edge of visibility'' ({{math|<var>t</var>{{=}}{{sfrac|80|20}}+1}}), ''will keep drivers in compliance with the ACDA rule in most simple highway driving conditions – day or night'' – with growing error towards safety at lower speeds.

On final note, slope has an effect on stopping distance. An additional second or so will need to be added when stopping while traveling down a steep incline, and conversely driving uphill will improve breaking.<ref name="AASHTO"/> This is accounting that a level road was assumed in the rule of thumb. [[Assured clear distance ahead#Case 1: Safe speed as a function of forward line-of-sight|See more general derivation here]]
{{hidden end}}

==Tables of reference constants and safe speeds==
===Reference constants===
====Table of perception-reaction times====
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
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|title=Table of perception-reaction times
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{| class="wikitable"
|+ '''Perception-reaction times [seconds]<ref name="Taoka"/><ref name="NCHRP">{{cite book |title=NCHRP Report 400: Determination of Stopping Sight Distances |author=National Cooperative Highway Research Program |publisher=Transportation Research Board (National Academy Press) |chapter=2 |page=24 |year=1997 |isbn=978-0-309-06073-8 |chapter-url=http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_400.pdf}}</ref>'''
|-
! Anticipated object !! Unexpected object !! Unexpected signal
|-
| 0.72 || 1.28 || 1.27
|}

{{hidden end}}

====Table of tire-roadway friction coefficients====
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
|toggle=left
|title=Table of tire-roadway friction coefficients
}}

{| class="wikitable"
|+'''Average value of tire friction coefficient<ref>{{cite book |title=Theory of ground vehicles |author=J.Y. Wong |edition=2 |date=1993 |page=26 |publisher=Wiley |isbn=9780471524960 |url=https://books.google.com/books?id=Blp2D1DteTYC }}</ref>'''
|-
! Road surface !! Peak value (''μ''<sub>s</sub>) !! Sliding value (''μ''<sub>d</sub>)
|-
| Asphalt and concrete (dry) || 0.80 − 0.90 || 0.75
|-
| Asphalt (wet) || 0.50 − 0.70 || 0.45 − 0.60
|-
| Concrete (wet) || 0.80 || 0.70
|-
| Gravel || 0.60 || 0.55
|-
| Earth road (dry) || 0.68 || 0.65
|-
| Earth road (wet) || 0.55 || 0.40 − 0.50
|-
| Snow (hard-packed) || 0.20 || 0.15
|-
| Ice || 0.10 || 0.07
|}

See also [http://hpwizard.com/tire-friction-coefficient.html Tire friction and rolling resistance coefficients]
{{hidden end}}

====Table of acceleration values====
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
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|title=Table of acceleration values
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{| class="wikitable"
|+'''Acceleration values<ref name="J. Stannard Baker"/>'''
|-
! Car !! Truck !! Bicycle
|-
| 0.15g || 0.085–0.138g<ref>{{cite journal |journal=SAE Technical Paper |volume=1 |title=Analysis of Acceleration in Passenger Cars and Heavy Trucks |author1=C. Proctor |author2=W. Grimes |display-authors=etal |doi=10.4271/950136 |quote=Based on the time and distance measurements for the 219 trucks, calculated average accelerations were 0.085, 0.106, and 0.138 g's over the first 50 ft for the flatbed, box, and bobtail configurations, respectively.|series=SAE Technical Paper Series |year=1995 }}</ref> || 
|}

See [https://web.archive.org/web/20160518025856/http://www.automobile-catalog.com/ Car specific accelerations]
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====Table of intercept values====
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
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|title=Table of intercept values
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{| class="wikitable"
|+'''Approach speeds of hazards which may foreseeably intercept the roadway'''
|-
! pedestrian(walk/run) !! bicycle !! cat !! dog !! deer !! elk
|-
| 3.1–5.6&nbsp;mph/27.78&nbsp;mph<ref name=Browning2006>{{cite journal |author=Browning, R. C. |author2=Baker, E. A. |author3=Herron, J. A. |author4=Kram, R.| title=Effects of obesity and sex on the energetic cost and preferred speed of walking |journal= Journal of Applied Physiology |volume= 100 |issue=2 |pages= 390–398|year=2006 | doi=10.1152/japplphysiol.00767.2005 | pmid=16210434}}</ref> || 14.7f/s<ref>{{cite web |url=http://www.dot.ca.gov/hq/traffops/engineering/mutcd/ca_mutcd2014.htm |title=CAMUTCD |publisher=California Department of Transportation |page=984 |quote=a bicyclist riding a bicycle 6 feet long to clear the last conflicting lane at a speed of 14.7 feet/sec }}</ref> || 29.8&nbsp;mph || 63.5&nbsp;km/h || 48.2&nbsp;km/h || 72.4&nbsp;km/h
|}

See more [http://speedofanimals.com/ animal intercept speeds]. See article on [[Speed#Examples of different speeds|speed]].

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====Table of tire speed ratings====
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
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|title=Table of tire speed ratings
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{| class="wikitable"
|+'''Tire speed rating<ref name="etrto.org">{{cite web |url=http://www.etrto.org/files/files/ETRTO/Index_Publications_SM/SM_2010_GEN_INFO.pdf |title=European Tyre and Rim Technical Organisation Standards Manual 2010 G6 |publisher=The European Tire and Rim Technical Organization }}{{dead link|date=November 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>'''
|-
!'''Code'''!!'''mph'''!!'''km/h'''!!!!'''Code'''!!'''mph'''!!'''km/h'''
|-
! A1
| 3 || 5 ||
! L 
| 75 || 120
|-
! A2
| 6 || 10 ||
! M
| 81 || 130
|-
! A3
| 9 || 15 ||
! N
| 87 || 140
|-
! A4
| 12 || 20 ||
! P
| 94 || 150
|-
! A5
| 16 || 25 ||
! Q
| 100 || 160
|-
! A6
| 19 || 30 ||
! R
| 106 || 170
|-
! A7
| 22 || 35 ||
! S
| 112 || 180
|-
! A8
| 25 || 40 ||
! T
| 118 ||190
|-
! B
| 31 || 50 ||
! U
| 124 || 200
|-
! C
| 37 || 60 ||
! H
| 130 || 210
|-
! D
| 40 || 65 ||
! V
| 149 || 240
|-
! E
| 43 || 70 ||
! Z
| over 149 || over 240
|-
! F
| 50 || 80 ||
! W
| 168 || 270
|-
! G
| 56 || 90 ||
!(W)
| over 168 || over 270
|-
! J
| 62 || 100 ||
!Y
|186 ||300
|-
! K
| 68 || 110 ||
!(Y)
| over 186 || over 300
|}

See article on [[tire code]]s.

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===Safe speeds===
====Table of ACDA: forward line-of-sight====
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}}

{| class="wikitable"
|+'''Average safe speed as a function of assured clear distance ahead<ref name="VA Table">{{cite web |url=http://law.lis.virginia.gov/vacode/46.2-880/ |title=Tables of speed and stopping distances |publisher=The State of Virginia}}</ref>'''
|-
! ACDA [meters] !! ACDA [feet] !! Safe speed [km/h] !! Safe speed [mph]
|-
| 1 || 3.3 || 2.3 || 1.4
|-
| 2.5 || 8.2 || 5.6 || 3.5
|-
| 4 || 13.1 || 8.6 || 5.3
|-
| 5.5 || 18.0 || 11.4 || 7.1
|-
| 7 || 23.0 || 14.1 || 8.8
|-
| 8.5 || 27.9 || 16.7 || 10.4
|-
| 10 || 32.8 || 19.1 || 11.9
|-
| 15 || 49 || 27 || 16
|-
| 30 || 98 || 45 || 28
|-
| 45 || 148 || 60 || 37
|-
| 60 || 197 || 73 || 45
|-
| 75 || 246 || 84 || 52
|-
| 90 || 295 || 95 || 59
|-
| 105 || 344 || 105 || 65
|-
| 120 || 394 || 114 || 71
|-
| 135 || 443 || 122 || 76
|-
| 150 || 492 || 130 || 81
|-
| 165 || 541 || 138 || 86
|-
| 180 || 591 || 146 || 91
|-
| 195 || 640 || 153 || 95
|-
| 210 || 689 || 160 || 99
|-
| 225 || 738 || 166 || 103
|-
| 240 || 787 || 173 || 107
|-
| 255 || 837 || 179 || 111
|-
| 270 || 886 || 185 || 115
|-
| 285 || 935 || 191 || 119
|-
| 300 || 984 || 197 || 122
|}

The speed values in this table are produced from the formula using an "average" coefficient of friction (μ) of 0.7, and a perception-reaction time of 1.5 seconds. Speed values specific to a given circumstance can be obtained with the same formula using the appropriate reference constants specific to the circumstance.
:<math>V_{BSL}= \sqrt{(\mu +e)^2 g^2 t_{prt}^2+ 2 (\mu + e) g d_{ACDA_s} } - (\mu+e) g t_{prt}</math>

{{hidden end}}

====Table of ACDA: horizontal line-of-sight====
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
|toggle=left
|title=Table of ACDA: horizontal line-of-sight
}}

{| class="wikitable"
|+'''Safe speed as a function of horizontal clearance for 9&nbsp;km/h (5.6&nbsp;mph) intercept object (i.e. child)'''
|-
! HSD [meters] !! HSD [feet] !! Safe speed [km/h] !! Safe speed [mph]
|-
| 3.0 || 10 || 0 || 0
|-
| 4.0 || 13.1 || 4.9 || 3.1
|-
| 4.5 || 14.8 || 14.8 || 9.2
|-
| 5.0 || 16.4 || 24.7 || 15.4
|-
| 5.5 || 18.0 || 34.6 || 21.5
|-
| 6 || 20 || 44 || 28
|-
| 7 || 23 || 64 || 40
|-
| 8 || 26 || 84 || 52
|-
| 9 || 30 || 104 || 65
|-
| 10 || 33 || 124 || 77
|-
| 11 || 36 || 143 || 89
|-
| 12 || 39 || 163 || 101
|}
This table demonstrates why [[alley]]ways, [[parking lots]], [[parks]], and [[residential areas]] frequently set 5–15&nbsp;mph speed limits when the side clearance from the road is less than 15 feet. An urban or residential street which permits a maximum speed limit of 25&nbsp;mph under its very best conditions (roadsides cleared of visual obstructions past a 20-foot maintained [[Right-of-way (property access)|right of way]]), may in practice be unsafe to drive at more than 10&nbsp;mph within sections with utilized curbside parking. This table also suggests that the safe speed could be greater than a statutory 25&nbsp;mph posted speed, where roadside clearance is sufficient such that no "foreseeable" object could emerge from the proximate edge of roadside visibility, transect the cleared area, and intercept the lane before the driver could come to a halt. However, wary road design engineers may have differing views of foreseeable intercept speeds than that reflected by the 85th percentile speed chosen by the public. This can have unfortunate consequences where a mass commuting public is unfamiliar with or does not appreciate specific local hazards. Narrow lane widths are purposely used for [[traffic calming]], because careful drivers universally choose their speed depending on the roadway width.<ref>{{cite web |url=http://nacto.org/publication/urban-street-design-guide/street-design-elements/lane-width/ |title=Urban Street Design Guide: Lane Width |date=11 July 2013 |publisher=National Association of City Transportation Officials |quote=as the width of the lane increased, the speed of the roadway increased}}</ref> Standard horizontal clearances are commonly set by [[AASHTO]] guidelines or a jurisdiction's department of transportation.<ref name="AASHTO"/><ref>{{cite web |url=http://www.dot.ca.gov/hq/oppd/hdm/pdf/english/chp0300.pdf |title=CAHDM |pages=300–25 |quote=309.1 Horizontal Clearances for Highways: The horizontal clearance to all roadside objects should be based on engineering judgment with the objective of maximizing the distance between roadside objects and the edge of traveled way.}}</ref>

{| class="wikitable"
|+'''Safe speed as a function of horizontal clearance for 16&nbsp;km/h (10&nbsp;mph) intercept object (i.e. domestic animals)'''
|-
! HSD [meters] !! HSD [feet] !! Safe speed [km/h] !! Safe speed [mph]
|-
| 7 || 23 || 4 || 2
|-
| 8 || 26 || 15 || 9
|-
| 9 || 30 || 26 || 16
|-
| 10 || 33 || 37 || 23
|-
| 11 || 36 || 48 || 30
|-
| 12 || 39 || 59 || 37
|-
| 13 || 43 || 70 || 44
|-
| 14 || 46 || 82 || 51
|-
| 15 || 49 || 93 || 58
|-
| 16 || 52 || 104 || 65
|-
| 17 || 56 || 115 || 71
|-
| 18 || 59 || 126 || 78
|-
| 19 || 62 || 137 || 85
|-
| 20 || 66 || 148 || 92
|-
| 21 || 69 || 159 || 99
|-
| 22 || 72 || 171 || 106
|-
| 23 || 75 || 182 || 113
|-
| 24 || 79 || 193 || 120
|-
| 25 || 82 || 204 || 127
|}

{| class="wikitable"
|+'''Safe speed as a function of horizontal clearance for 48.2&nbsp;km/h (30&nbsp;mph) intercept object (i.e. deer)'''
|-
! HSD [meters] !! HSD [feet] !! Safe speed [km/h] !! Safe speed [mph]
|-
| 20 || 66 || 0 || 0
|-
| 21 || 69 || 3 || 2
|-
| 22 || 72 || 7 || 4
|-
| 23 || 75 || 11 || 7
|-
| 24 || 79 || 14 || 9
|-
| 25 || 82 || 18 || 11
|-
| 26 || 85 || 22 || 14
|-
| 27 || 89 || 26 || 16
|-
| 28 || 92 || 29 || 18
|-
| 29 || 95 || 33 || 20
|-
| 30 || 98 || 37 || 23
|-
| 31 || 102 || 40 || 25
|-
| 32 || 105 || 44 || 27
|-
| 33 || 108 || 48 || 30
|-
| 34 || 112 || 51 || 32
|-
| 35 || 115 || 55 || 34
|-
| 36 || 118 || 59 || 37
|-
| 37 || 121 || 62 || 39
|-
| 38 || 125 || 66 || 41
|-
| 39 || 128 || 70 || 43
|-
| 40 || 131 || 74 || 46
|-
| 41 || 135 || 77 || 48
|-
| 42 || 138 || 81 || 50
|-
| 43 || 141 || 85 || 53
|-
| 44 || 144 || 88 || 55
|-
| 45 || 148 || 92 || 57
|-
| 46 || 151 || 96 || 59
|-
| 47 || 154 || 99 || 62
|-
| 48 || 157 || 103 || 64
|-
| 49 || 161 || 107 || 66
|-
| 50 || 164 || 110 || 69
|}

The speed values in these tables are produced from the formula using an "average" coefficient of friction (μ) of 0.7, and a perception-reaction time of 1.5 seconds. Speed values specific to a given circumstance can be obtained with the same formula using the appropriate reference constants specific to the circumstance.
:<math>V_{BSL}=2 g (\mu + e) (\frac{d_{hsd}}{v_i}-t_{prt})</math>

{{hidden end}}

====Table of ACDA: intersectional setback====
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
|toggle=left
|title=Table of ACDA: intersectional setback
}}

{| class="wikitable"
|+'''Approach speed as a function of setback distance (acceleration=0.15g)<ref>{{cite book |title=California Highway Design Manual |publisher=California Department of Transportation |chapter=405.1 |pages=400–14 |year=2012 |chapter-url=http://www.dot.ca.gov/hq/oppd/hdm/hdmtoc.htm |quote= Set back for the driver of the vehicle on the crossroad shall be a minimum of 10 feet plus the shoulder width of the major road but not less than 15 feet.}}</ref>'''
|-
! Setback [meters] !! Setback [feet] !! Approach speed [m/s]
|-
| 0 || 0 || 0
|-
| 0.5 || 1.6 || 11.3
|-
| 1 || 3 || 16
|-
| 1.5 || 4.9 || 19.6
|-
| 2 || 7 || 23
|-
| 3 || 10 || 28
|-
| 4 || 13 || 32
|-
| 5 || 16 || 36
|-
| 6 || 20 || 39
|-
| 8 || 26 || 45
|-
| 10 || 33 || 51
|-
| 12 || 39 || 55
|-
| 14 || 46 || 60
|-
| 16 || 52 || 64
|-
| 18 || 59 || 68
|-
| 20 || 66 || 72
|-
| 22 || 72 || 75
|-
| 24 || 79 || 78
|-
| 26 || 85 || 82
|-
| 28 || 92 || 85
|-
| 30 || 98 || 88 
|}

Speed values specific to a given circumstance can be obtained with the same formula using the appropriate reference constants specific to the circumstance.
:<math>V_{BSL}=2 g (\mu + e )\left(\sqrt{\frac{2 d_{sl}}{a_i}} + t_{pc} - t_{prt} \right)</math>

{{hidden end}}

====Table of following distances====
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
|toggle=left
|title=Table of following distances (2 second rule)
}}

{| class="wikitable"
|+'''Following distance (2 second rule)'''
|-
! Speed [km/h] !! Speed [mph] !! Following distance [meters] !! Following distance [feet]
|-
| 0 || 0 || 0 || 0
|-
|5 || 3 || 3 || 9
|-
|10 || 6 || 6 || 18
|-
|15 || 9 || 8 || 27
|-
|20 || 12 || 11 || 36
|-
|25 || 16 || 14 || 46
|-
|30 || 19 || 17 || 55
|-
|35 || 22 || 19 || 64
|-
|40 || 25 || 22 || 73
|-
|45 || 28 || 25 || 82
|-
|50 || 31 || 28 || 91
|-
|55 || 34 || 31 || 100
|-
|60 || 37 || 33 || 109
|-
|65 || 40 || 36 || 118
|-
|70 || 43 || 39 || 128
|-
|75 || 47 || 42 || 137
|-
|80 || 50 || 44 || 146
|-
|85 || 53 || 47 || 155
|-
|90 || 56 || 50 || 164
|-
|95 || 59 || 53 || 173
|-
|100 || 62 || 56 || 182
|-
|105 || 65 || 58 || 191
|-
|110 || 68 || 61 || 200
|-
|115 || 71 || 64 || 210
|-
|120 || 75 || 67 || 219
|-
|125 || 78 || 69 || 228
|-
|130 || 81 || 72 || 237
|-
|135 || 84 || 75 || 246
|-
|140 || 87 || 78 || 255
|-
|145 || 90 || 81 || 264
|-
|150 || 93 || 83 || 273
|}

{{hidden end}}

====Table of critical speeds====
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
|toggle=left
|title=Table of critical speeds
}}

{| class="wikitable"
|+'''Average physical critical speeds on level surface (e=0, μ=0.7)'''
|-
! Radius [meters] !! Radius [feet] !! Safe speed [km/h] !! Safe speed [mph] 
|-
| 5 || 16.4 || 21.1 || 13.1
|-
| 10 || 33 || 30 || 19
|-
| 20 || 66 || 42 || 26
|-
| 30 || 98 || 52 || 32
|-
| 40 || 131 || 60 || 37
|-
| 50 || 164 || 67 || 41
|-
| 60 || 197 || 73 || 45
|-
| 70 || 230 || 79 || 49
|-
| 80 || 262 || 84 || 52
|-
| 90 || 295 || 89 || 56
|-
| 100 || 328 || 94 || 59
|-
| 110 || 361 || 99 || 61
|-
| 120 || 394 || 103 || 64
|-
| 130 || 427 || 108 || 67
|-
| 140 || 459 || 112 || 69
|-
| 150 || 492 || 116 || 72
|-
| 160 || 525 || 119 || 74
|-
| 170 || 558 || 123 || 76
|-
| 180 || 591 || 127 || 79
|-
| 190 || 623 || 130 || 81
|-
| 200 || 656 || 133 || 83
|}

The speed values in this table are produced from the formula using an "average" coefficient of friction (''μ'') of 0.7 and zero [[Cant (road/rail)|superelevation]]. Speed values specific to a given circumstance can be obtained with the same formula using the appropriate reference constants specific to the circumstance.

{| class="wikitable"
|+'''Average psychological critical speeds on level surface (''e''7&nbsp;=&nbsp;0, ''μ''&nbsp;=&nbsp;0.3)<ref name="Glennon-Hill"/>'''
|-
! Radius [meters] !! Radius [feet] !! Safe speed [km/h] !! Safe speed [mph] 
|-
| 5 || 16 || 14 || 9
|-
| 10 || 33 || 20 || 12
|-
| 15 || 49 || 24 || 15
|-
| 20 || 66 || 28 || 17
|-
| 25 || 82 || 31 || 19
|-
| 30 || 98 || 34 || 21
|-
| 35 || 115 || 37 || 23
|-
| 40 || 131 || 39 || 24
|-
| 45 || 148 || 41 || 26
|-
| 50 || 164 || 44 || 27
|-
| 55 || 180 || 46 || 28
|-
| 60 || 197 || 48 || 30
|-
| 65 || 213 || 50 || 31
|-
| 70 || 230 || 52 || 32
|-
| 75 || 246 || 53 || 33
|-
| 80 || 262 || 55 || 34
|-
| 85 || 279 || 57 || 35
|-
| 90 || 295 || 59 || 36
|-
| 95 || 312 || 60 || 37
|-
| 100 || 328 || 62 || 38
|-
| 105 || 344 || 63 || 39
|-
| 110 || 361 || 65 || 40
|-
| 115 || 377 || 66 || 41
|-
| 120 || 394 || 68 || 42
|-
| 125 || 410 || 69 || 43
|-
| 130 || 427 || 70 || 44
|-
| 140 || 459 || 73 || 45
|-
| 145 || 476 || 74 || 46
|-
| 150 || 492 || 76 || 47
|-
| 155 || 509 || 77 || 48
|-
| 160 || 525 || 78 || 49
|-
| 170 || 558 || 81 || 50
|-
| 175 || 574 || 82 || 51
|-
| 180 || 591 || 83 || 51
|-
| 185 || 607 || 84 || 52
|-
| 190 || 623 || 85 || 53
|-
| 200 || 656 || 87 || 54
|-
| 205 || 673 || 88 || 55
|-
| 210 || 689 || 89 || 56
|-
| 220 || 722 || 92 || 57
|-
| 230 || 755 || 94 || 58
|-
| 240 || 787 || 96 || 59
|-
| 245 || 804 || 97 || 60
|-
| 250 || 820 || 98 || 61
|-
| 260 || 853 || 100 || 62
|-
| 280 || 919 || 103 || 64
|-
| 300 || 984 || 107 || 66
|-
| 320 || 1050 || 110 || 69
|-
| 340 || 1115 || 114 || 71
|-
| 360 || 1181 || 117 || 73
|-
| 380 || 1247 || 120 || 75
|-
| 400 || 1312 || 124 || 77
|-
| 420 || 1378 || 127 || 79
|-
| 440 || 1444 || 130 || 80
|-
| 460 || 1509 || 132 || 82
|-
| 480 || 1575 || 135 || 84
|-
| 500 || 1640 || 138 || 86 
|}

Most motorists will not tolerate a lateral acceleration exceeding 0.3g (μ=0.3) above which many will panic.<ref name="Glennon-Hill"/>

Speed values specific to a given circumstance can be obtained with the same formula using the appropriate reference constants specific to the circumstance.
:<math>V_{BSL}=\sqrt{ \frac{(\mu+e) g r}{1-\mu e}}</math>
{{hidden end}}

===Table of detection thresholds===
{{Hidden begin|titlestyle = text-align: right; font-size:100%; padding-right:2.5em;|contentstyle = text-align: left; padding-left:3em; 
|toggle=left
|title=Table of detection thresholds: SAVT
}}

{| class="wikitable"
|+'''Table of detection thresholds: looming motion of a car {{math|&theta;<sub>t</sub>{{=}}0.0397-0.0117, S{{=}}6ft}}'''<ref name="Hoffmann & Mortimer"/><ref name="Maddox"/><ref name="Markkula et al">{{cite journal |last1=Markkula |first1=Gustav |last2=Engström |first2=Johan |last3=Lodin |first3=Johan |last4=Bärgman |first4=Jonas |last5=Victor |first5=Trent |title=A farewell to brake reaction times? Kinematics-dependent brake response in naturalistic rear-end emergencies |journal=Accident Analysis & Prevention |volume=95 |issue=A |pages=209–226 |date=October 2016 |url=http://eprints.whiterose.ac.uk/102162/1/A%20farewell%20to%20brake%20reaction%20times%20-%202016-06-23%20-%20for%20self-archiving.pdf |doi=10.1016/j.aap.2016.07.007 |pmid=27450793 |quote=The data show that drivers do not reliably respond to looming until it reaches .02 rad/sec}}</ref><ref>{{cite web |title=The complete Catalog of Cars, car specs database |url=http://www.automobile-catalog.com/ |access-date=2015-12-05 |archive-url=https://web.archive.org/web/20160518025856/http://www.automobile-catalog.com/ |archive-date=2016-05-18 }}</ref>
|-
! Speed [KM/H] !! Speed [MPH] !! Detection distance [m] !! Detection distance [ft] !! Time to collision [s]
|-
| ||5|| ||33–61||5–8
|-
| ||10|| ||47–87||3–6
|-
| ||15|| ||58–106||3–5
|-
| ||20|| ||67–123||2–4
|-
| ||25|| ||74–137||2–4
|-
| ||30|| ||81–150||2–3
|-
| ||35|| ||88–162||2–3
|-
| ||40|| ||94–173||2–3
|-
| ||45|| ||100–184||2–3
|-
| ||50|| ||105–194||1–3
|-
| ||55|| ||110–203||1–3
|-
| ||60|| ||115–212||1–2
|-
| ||65|| ||120–221||1–2
|-
| ||70|| ||125–229||1–2
|-
| ||75|| ||129–237||1–2
|-
| ||80|| ||133–245||1–2
|}

{| class="wikitable"
|+'''Table of detection thresholds: looming motion of tractor-trailer {{math|&theta;<sub>t</sub>{{=}}0.0397-0.0117, S{{=}}8ft}}'''<ref name="Hoffmann & Mortimer"/><ref name="Maddox"/><ref name="Markkula et al"/>
|-
! Speed [KM/H] !! Speed [MPH] !! Detection distance [m] !! Detection distance [ft] !! Time to collision [s]
|-
| ||5|| ||38–71||5–10
|-
| ||10|| ||54–100||4–7
|-
| ||15|| ||66–123||3–6
|-
| ||20|| ||77–142||3–5
|-
| ||25|| ||86–158||2–4
|-
| ||30|| ||94–173||2–4
|-
| ||35|| ||102–187||2–4
|-
| ||40|| ||109–200||2–3
|-
| ||45|| ||115–212||2–3
|-
| ||50|| ||121–224||2–3
|-
| ||55|| ||127–235||2–3
|-
| ||60|| ||133–245||2–3
|-
| ||65|| ||139–255||1–3
|-
| ||70|| ||144–265||1–3
|-
| ||75|| ||149–274||1–2
|-
| ||80|| ||154–283||1–2
|}

For a person with SAVT limit of <math>\dot\theta_t</math>, the looming motion of a directly approaching object of size {{math|<var>S</var>}}, moving at velocity {{math|<var>v</var>}}, is not detectable until its distance {{math|<var>D</var>}} is<ref name="Weinberger"/>
:<math>D \lessapprox \sqrt{\frac{S \cdot v}{\dot{\theta_{t}}}-\frac{S^2}{4}}</math>
{{hidden end}}

==See also==
* [[Advisory speed limit]]
* [[Assumption of risk]]
* [[Speed limit#Basic rule|Basic speed rule]]
* [[Braking distance]]
* [[Following distance]]
* [[Calculus of negligence]]
* [[Duty of care]]
* [[Geometric design of roads#Effects of insufficient sight distance|Effects of insufficient sight distance]]
* [[Herbert William Heinrich|Heinrich's Law]]
* [[Illusory superiority]]
* [[International Regulations for Preventing Collisions at Sea#Section I .28Conduct of vessel in any condition of visibility.29|International Regulations for Preventing Collisions at Sea—Part B, Section I, Rule 6: Safe speed]]
* [[Road traffic safety]]
* [[Standard of care]]
* [[The man on the Clapham omnibus]]
* [[Two-second rule]]
* [[Visual flight rules]]
* ''[[Volenti non fit injuria]]''

==Notes==
{{Reflist|30em|group="Note"}}

==References==
{{reflist|30em}}

===Further reading: tertiary sources===
====ACDA related law reviews====
*{{anchor|75_ALR3d_327}}{{cite book |title=American Law Reports--Annotated, 3rd Series |chapter=Automobiles: sudden emergency as exception to rule requiring motorist to maintain ability to stop within assured clear distance ahead |author=James O. Pearson |publisher=The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company |volume=75 |page=327 |year=2009}}
*{{anchor|42_ALR2d_13}}{{cite book |title=American Law Reports--Annotated, 2nd Series |chapter=Liability for motor vehicle accident where vision of driver is obscured by smoke, dust, atmospheric condition, or unclean windshield|author=W. R. Habeeb|publisher=The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company |volume=42 |page=13 |year=2010}}
*{{anchor|64_ALR3d_760}}{{cite book |title=American Law Reports--Annotated, 3rd Series |chapter=Liability or recovery in automobile negligence action as affected by driver's being blinded by lights other than those of a motor vehicle |author=Wade R. Habeeb |publisher=The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company |volume=64 |page=760 |year=2009}}
*{{anchor|64_ALR3d_760}}{{cite book |title=American Law Reports--Annotated, 3rd Series |chapter=Liability or recovery in automobile negligence action as affected by driver's being blinded by lights of motor vehicle |author=Wade R. Habeeb |publisher=The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company |volume=64 |page=551 |date=c. 2009}}
*{{anchor|59_ALR2d_1202}}{{cite book |title=American Law Reports--Annotated, 2nd Series |chapter=Right and duty of motorist on through, favored, or arterial street or highway to proceed where lateral view at intersection is obstructed by physical obstacle |author=L. S. Tellier |publisher=The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company |volume=59 |page=1202 |year=2011}}
*{{anchor|133_ALR_967}}{{cite book |title=American Law Reports--Annotated |chapter="Assured clear distance" statute or rule as applied at hill or curve |publisher=The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company |volume=133 |page=967 }}
*{{anchor|31_ALR2d_1424}}{{cite book |title=American Law Reports--Annotated, 2nd Series |chapter=Application of "assured clear distance ahead" or "radius of lights" doctrine to accident involving pedestrian crossing the street or highway |publisher=The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company |volume=31|page=1424}}
*{{anchor|133_ALR_967}}{{cite book |title=American Law Reports--Annotated, 2nd Series |chapter=Driving automobile at speed which prevents stopping within range of vision as negligence |publisher=The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company |volume=44;58;87;97 |page=1403;1493;900;546 }}
*{{anchor|85_ALR_2d_613}}{{cite book |title=American Law Reports--Annotated, 2nd Series |chapter=Driver's failure to maintain proper distance from motor vehicle ahead |publisher=The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company |volume=85 |page=613}}
*{{anchor|32_ALR_4th_933}}{{cite book |title=American Law Reports--Annotated, 4th Series |chapter=Motor vehicle operator's liability for accident occurring while driving with vision obscured by smoke or steam |publisher=The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company |volume=32 |page=933}}
*{{anchor|22_ALR_2d_292}}{{cite book |title=American Law Reports--Annotated, 2nd Series |chapter=Duty and liability of vehicle driver blinded by glare of lights |publisher=The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company |volume=22 |page=292}}
*{{anchor|55_ALR_4th_822}}{{cite book |title=American Law Reports--Annotated, 4th Series |chapter=Liability for killing or injuring, by motor vehicle, livestock or fowl on highway |publisher=The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company |volume=55 |page=822}}
*{{anchor |Virginia Law Review}}{{cite journal |author=R. J. H. |title=The Uniform Motor Vehicle Act in Virginia |journal=Virginia Law Review |volume=23 |number=3 |pages=351–358 |date=January 1937 |doi=10.2307/1067282 |jstor=1067282}}
*{{anchor }}{{cite journal |author=D. M. Postlewaite |title=Negligence -- Doctrine of Assured Clear Distance Ahead -- Statute as Subjective Test |journal=Law Journal of the Student Bar Association of the Ohio State University |volume=1 |number=3 |pages=284–287 |year=1935 |issn=0048-1572 |hdl=1811/72043 }}
*{{anchor|California Law Review}}{{cite journal |author=Thomas Stanton |title=Negligence and Contributory Negligence Per Se: The "Range of Vision" and "Blinding Lights" Rules in Automobile Accident Cases |journal=California Law Review |volume=23 |number=5 |pages=498–506 |date=July 1935 |doi=10.2307/3476106 |jstor=3476106}}
*{{anchor}}{{cite journal |author=Myron L. Garon |title=Recent Developments in California's Last Clear Chance Doctrine |journal=California Law Review |volume=40 |number=3 |pages=404–411 |date=Autumn 1952 |doi=10.2307/3477930 |jstor=3477930|url=https://scholarship.law.berkeley.edu/californialawreview/vol40/iss3/4 }}
*{{anchor|Case Wester Law Review}}{{cite journal |author=Murray Carl Lertzman |title=The Assured Clear Distance Ahead Rule in Ohio |journal=Case Western Reserve Law Review |volume=5 |number=1 |pages=77–83 |date=1954 |url=http://scholarlycommons.law.case.edu/caselrev/vol5/iss1/7}}
*{{anchor |Michigan Law Review}}{{cite journal |author=Herbert A. Bernhard |title=Negligence: Breach of Duty: Assured Clear Distance Ahead Doctrine |journal=Michigan Law Review |volume=55 |number=2 |pages=299–301 |date=December 1956 |doi=10.2307/1285419 |jstor=1285419|url=https://repository.law.umich.edu/cgi/viewcontent.cgi?article=7140&context=mlr }}
*{{anchor |Louisiana Law Review}}{{cite journal |author=Winston R. Day |title=Assured Clear Distance Doctrine in Louisiana |journal=Louisiana Law Review |volume=30 |number=1 |pages=129–139 |date=December 1969 |url=http://digitalcommons.law.lsu.edu/lalrev/vol30/iss1/10}}
*{{anchor |Notre Dame Law Review}}{{cite journal |author1=Alfred A. Sniadowski |author2=John De Mots |author3=Charles S. Reddy |author4=Frank E. Bright |title=Recent Decisions |journal=Notre Dame Law Review |volume=13 |number=4 |date=1938 |url=http://scholarship.law.nd.edu/ndlr/vol13/iss4/5}}
*{{anchor |Nixon}}{{cite journal |author=Richard M. Nixon |title=Changing Rules of Liability in Automobile Accident Litigation |journal=Law and Contemporary Problems |volume=3 |number=4 |pages=476–490 |date=October 1936 |issn=0023-9186 |url=http://scholarship.law.duke.edu/lcp/vol3/iss4/3 |doi=10.2307/1189341|jstor=1189341 |author-link=Richard M. Nixon }}

====Other printed resources====
*{{anchor|Sklansky}}{{cite book |title=Evidence: Cases, Commentary and Problems |author=David A. Sklansky |publisher=Aspen Publishers |edition=3 |chapter=Ch.9,11,&12 |date= 2012-02-16 |isbn=9781454806820}}
*{{anchor|Green}}{{cite book |title=Forensic Vision with Application to Highway Safety |edition=3 |author=Marc Green |publisher=Lawyers & Judges Publishing Company, Inc. |page=454 |year=2008 |isbn=9781933264547 |url=https://books.google.com/books?id=lt7fAH0s7QYC&q=assured%20clear%20distance%20ahead&pg=PA44|display-authors=etal}}
*{{anchor|Baker}}{{cite book |title=Traffic Accident Investigator's Manual for Police |edition=2 |author=J. Stannard Baker |publisher=The Traffic Institute, Northwestern University |year=1963 |pages=44–48, 162–167 |lccn=62-20895}}
*{{anchor|AASHTO}}{{cite book |title=A Policy on Geometric Design of Highways and Streets |edition=6th |year=2011 |publisher=American Association of State Highway and Transportation Officials |isbn=978-1560515081 |url=https://bookstore.transportation.org/collection_detail.aspx?ID=110}}
*{{anchor|ITE}}{{cite book |title=Traffic Engineering Handbook |edition=7th |author1=Brian Wolshon |author2=Anurag Pande |publisher=Institute of Traffic Engineers |year=2015 |isbn=978-1-118-76230-1}}
*{{anchor|Glennon}}{{cite book |title=Roadway Safety and Tort Liability |edition=2 |publisher=Lawyers & Judges Publishing Company, Inc. |author1=John C. Glennon |author2=Paul F. Hill |date=2004 |isbn=978-1930056947}}
*{{anchor |NCHRP}}{{cite book |title=NCHRP Report 400: Determination of Stopping Sight Distances |author=National Cooperative Highway Research Program |publisher=Transportation Research Board (National Academy Press) |year=1997 |isbn=978-0-309-06073-8 |url=http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_400.pdf}}
*{{anchor |NCHRP}}{{cite book |title=2013 Traffic Safety Facts. Report No. DOT HS 812 139 |author=National Center for Statistics and Analysis |publisher=National Highway Traffic Safety Administration |location=Washington, DC |date=2015 |url=http://www-nrd.nhtsa.dot.gov/Pubs/812139.pdf}}
*{{anchor}}{{cite book |title=The Common Law |author=Oliver Wendell Holmes Jr. |publisher=[[Little, Brown and Company]] |date=1881 |chapter=Online Version |chapter-url=https://archive.org/stream/commonlaw00holmuoft|title-link=The Common Law (Holmes) |author-link=Oliver Wendell Holmes, Jr }}
*{{anchor}}{{cite book |title=Ancient Law |author=Henry James Sumner Maine |publisher=[[John Murray (publishing house)|John Murray]] |date=1861 |chapter=Online Version |chapter-url=https://archive.org/details/ancientlaw030840mbp/|title-link=Ancient Law |author-link=Henry James Sumner Maine }}

====Web resources====
*[http://hpwizard.com/braking.html#stopping-distance Formula for generalized stopping distance on level ground]
*[http://www-nrd.nhtsa.dot.gov/CATS/index.aspx U.S. National Highway Traffic Safety Administration—NCSA Publications & Data Requests]
*{{YouTube|id=3fea5NsvHW4|title=Instructive Video on Sight Distance}}
{{Traffic law}}
{{Autonomous cars and enabling technologies}}

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