Assured clear distance ahead

In legal terminology, the assured clear distance ahead (ACDA) is the distance ahead of any terrestrial 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.[1] 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.[2][3][4] The rule is a precautionary trivial burden required to avert the great probable gravity of precious life loss and momentous damage.[5][6][7] Satisfying the ACDA rule is necessary but not sufficient to comply with the more generalized basic speed law, and accordingly, it may be used as both a layman's criterion and judicial test for courts to use in determining if a particular speed is negligent, but not to prove it is safe.[8] 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.[9][10][11] The concept has transcended into accident reconstruction and engineering.[12]

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 basic speed rule,[13] 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.[2][3]

As the original common law driving rule preceding statutized traffic law,[13] 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,[14] cyclist, and pedestrian–as well as natural hazards which may occupy or obstruct the roadway beyond the edge of visibility,[14] 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.[13][15] Furthermore, modern knowledge of human factors has revealed physiological limitations–such as the 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 statutes by staying clear of roadway.[16][17]

As common law rule or statute


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 reasoned general common sense rules of conduct of which naturally follow from the repetitive process of determining specific culpability.[18][5][19][20][21][22] Legislation often subsequently followed which either superfluously codified and endorsed or revised these principles,[23][24] of which courts would in turn continue to flesh out the details.[25][26][27] 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,[28][29] with differing jurisdictions adopting the language to carry its same effects.[30][31] Much of the earliest published record naturally pertains to high stakes wrecks[18][21] among vessels[32] or vehicles[33] as defined in those times, though the obvious principle applies to chariots and might in fact be time immemorial.[13][34][35]


Horses may still be expected to use the roadways, as well bicycles and automobiles.[36][37][38] The former are a regular appearance in both urban areas and in the country, and are commonly exercised by commuters and Amish. Many roads are unchanged since the 1800s while controlled-access highways have been invented specifically for the automobile.[39] Ships now have marine radar that allows one to view tens of miles beyond the eye. "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."[4][13] Decisional law usually settles the circumstances by which a portion of the roadway is assuredly clear without it being mentioned in statute.[2] States where the judiciary has explicitly established the state's ACDA law include Indiana,[40] Iowa,[27] Kansas,[41] Louisiana,[42][43] Michigan,[44][45][46] New York,[47] North Carolina,[14] Ohio,[26][48] Tennessee,[22][49] Vermont,[50] Wisconsin,[21][51] and California.[52][53][15][54][55]

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 presumption of negligence. States with such explicit ACDA standard of care provisions include: Iowa,[56] Michigan,[57] Ohio,[58] Oklahoma,[59] Pennsylvania,[60] and Texas.[61]

States which apply the principle by statute to watercraft on navigable waterways include all 174 member states of the International Maritime Organization,[62] notwithstanding membership: Great Britain and its common law inheriting Commonwealth of Nations,[18][19] The United States,[5][20][25] Florida,[63] Hawaii,[64] Illinois,[65] Louisiana,[66] Michigan,[67] Montana,[68] Oregon,[69] Texas,[70] and West Virginia.[71]

Most state-issued and some Canadian driver handbooks either instruct or mention the ACDA rule as required care or safe practice.[1][72][73][74][75][76][77][78]

Explicit ACDA statutes and regulations,[79] 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[11] 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[80][81] that has been brought about by recent technological and social changes such as event data recorders,[82][83] dashcams, self-driving cars,[84][12] safe cities and multi-use movements,[85][86][87][88][89][90][91][92][93][94][95] and a movement to reduce claims by speeders against governments for "dangerous conditions" when operating speeds exceed a roads inferred design speed.[96]

Collision liability has historically benefited the law profession by being cloaked as a mixture of fact and law, but with EDR's precisely preserving "a state of facts" often repeated with differing trial outcomes, collisions are less a question of fact, but of law.[80][81][97][98][99] 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.[100][101][102][103] Furthermore, the law needs to be clear, precise, and uniform[104][105] at a national level for the panoply of automobile manufacturers with the strict liability for their programming of law-abiding self-driving vehicles.[84][12] It is foreseeable that two self-driving car makes can collide because their algorithm of the law letter is different;[84] 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.[106]

Determining the ACDA

Static ACDA

Forward "line-of-sight" distance

Prima Facie Maximum Speed vs. "Line-of-Sight" Distance[107]
Permitted by good tires and clean, dry, level, pavement.

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 atmospheric opacity,[108] blinding glare,[109] darkness,[1][110] road design,[111][112] and adjacent environmental hazards including civil and recreational activities,[13] horse-drawn vehicle,[37] ridden animal,[37] livestock,[37] deer,[113] crossing traffic,[15] and parked cars. The ACDA may also be somewhat attenuated on roads with lower functional classification.[114][13][112] 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.[115][Note 1] 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.[115] During times of darkness, commercial vehicles can see ahead about 250 feet with low beams, and about 350–500 feet with high beams.[1] This clear distance corresponds to a maximum safe speed of 52 mph and 65-81 mph respectively on dry pavement with good tires,[107][116] which is attenuated further by convex and lateral road curvature; safe speed is always dynamic. Non-commercial vehicles have even shorter lighting distances.[116] Drivers commonly drive the maximum posted speed limit at night, often in violation of the ACDA rule[116][110][46][108] and this shows up in accident data.[117][3]

Head-on Car Speed vs. Detection Distance of Looming Motion[17]
For an onlooker without assistance of lateral movement.[118][119]
Lateral Car Speed vs. Detection Distance of Lateral Motion[120]
For an onlooker without assistance of looming movement.[118][119]

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[121][122] and bike paths[123] they create because of potential hazards.[124][125][54][126][127][128] This jurisprudence arises in-part because of the known difficulty in estimating the distance and velocity of an approaching vehicle,[128][118][119] which is psychophysically explained by its small angular size and belated divergence from an asymptotically null rate of expansion, which is beyond the subtended angular velocity detection threshold (SAVT) limits of visual acuity[129][130][131][16][17] by way of the Stevens' power law[16] and Weber–Fechner law, until the vehicle may be dangerously close; subjective constancy and the visual angle illusion[132] may also play a role.[Note 2][Note 3] Vehicles that are approaching an intersection from beyond the 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,[9][119] and any legal expectation to the contrary would implicate violating the vagueness doctrine of the US Constitution.[9][Note 4] It is the duty of the through-driver to slow down[133][125][54][126] and apply the ACDA principle specifically to the intersection.[1][13][35][112][15] See Table of detection thresholds.

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.[106][138] 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.[138] 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.[113][138] 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 "dhsd" affects the ACDA because the time ti=dhsd/Vi it takes for an intercepting object, animal, pedestrian, or vehicle with speed "Vi" to transverse this distance after emerging from the proximate edge of lateral visibility affords a vehicle with speed "V" a clear distance of "V*ti." Thus, the assured clear intercept distance "ACDAsi" is:

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 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: dACDA=tgapv. 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.[4] A common way to violate the dynamic ACDA is by tailgating.


The most accurate way to determine the ACDA is to directly measure it. Whereas this is impractical, 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 GIS, such as by properly 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.[139] Self-driving cars[12][140] may have a higher safe speed than human driven vehicles for a given ACDA where computer perception-reaction times are nearly instantaneous.


The Assured Clear Distance Ahead can be subjective to the baseline estimate of a 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 visually obstructed intersection as law.[13][112][115][128] 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 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.[118] Motor vehicle operators of average intelligence[81][141] are constantly required to utilize their 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.[53][142] 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 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.[142] 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.[126][141]

Seconds of distance to stop rule

Drivers and law enforcement alike can apply elementary level arithmetic[143] 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 "v" in miles per hour, this rule of thumb is as follows:

If this distance is greater than the ACDA, they need to slow down. While most experienced drivers develop a broad intuition required by everyday braking,[142] 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 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 (VBSL) under the basic speed law, without which the maximum safe speed cannot be determined. As mathematical statements are more precise than verbal statements alone,[144] the relation of the ACDA as a subset of the basic speed rule for land based vehicles may be objectively quantified as follows:

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 angles it approximates the road's percent grade divided by one hundred.

[Note 5]

The maximum velocity permitted by the Assured Clear Distance Ahead is controlling of safe speed (VBSL) for only the top and two cases. Safe speed may be greater or less than the actual legal speed limit depending upon the conditions along the road.[124]

[Note 6]

See reference VBSL 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 , the friction coefficient is symbolized by —and itself a function of the tire type and road conditions, the distance is the static ACDA, the constant is the acceleration of gravity, and interval is the perception-reaction time—usually between 1.0 and 2.5 seconds.[145][146]

See 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 Vi, can intercept after having emerged and traveled across the horizontal sight distance "dhsd." 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,[113] elk, moose, and antelope are more likely to intercept a roadway at over 30 mph (48 kph). Wildlife will frequently transit across a road before a full stop is necessary, however collisions with large 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 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 controlled drivers to be able pass through the intersection without danger of collision.[126][147] 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 ai, from a stop at a limit line a distance dsl away.[137]

ACDA: following distance

The pedantic fourth case applies when the dynamic ACDA "following distance" (dACDAd) is less than the static ACDA "line-of-sight" distance (dACDAs). 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" tg 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 Table of 2-second following distances

Critical speed

In the fifth case, critical speed Vcs applies when road curvature is the factor limiting safe speed. A vehicle which exceeds this speed will slide out of its lane. Critical speed is a function of curve radius r, superelevation or banking e, and friction coefficient μ;[124] the constant g again is the acceleration of gravity. However, most motorists will not tolerate a lateral acceleration exceeding 0.3g (μ = 0.3) above which many will panic.[148] Hence, critical speed may not resemble loss of control speed.[148] Attenuated "side" friction coefficients are often used for computing critical speed.[138] 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.[138][149] 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 to slow down when approaching an intersection.[125][54]

See Table of curvatures and critical speeds

Surface control

The bottom case is invoked when the maximum velocity for surface control Vcl 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, hydroplaning, roll center, fishtailing, jackknife tendencies, potholes, washboarding, frost heaving,[150] and tire speed rating are other factors limiting Vcl.

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[151] used by traffic engineers in establishing speed zones.[124][134][152][153] Fog, snow, or ice can create conditions where most people drive too fast, and chain reaction accidents in such conditions are examples of where large groups of drivers collided because they failed to reduce speed for the conditions.[124][154] The speeds at which most people drive can only be a very rough guide to safe speed,[124] and an illegal or negligent custom or practice is not in itself excusable.[155][81][156][80] Safe speed approximates the inferred design speed adjusted for environmental alterations and vehicle and person specific factors when VACDAs is the limiting factor.[157] 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.[154]

Relationship of posted speed limits to the explicitness of driver care standard

2005 winter road dipped beam
Distance seen with ECE light by night

Many people are challenged by the concept of unsafe speed because they find it vague and arbitrary.[11] It is well known that people instead resolve such challenges by attribute substitution,[158] 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 mph of the 85th-percentile speed of free-flowing traffic.[106][134][152][153][159] 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.[1][72][73][74] If drivers were mindful of the ACDA, the operating speed would by definition not exceed the inferred design speed.[106][153] 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;[1] 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 mph at night.[116][117][110][160][3][46]

"Assurance" beyond proximate edge of clear visibility as transference of liability

A general principle in 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 duty such as the exercise of proper care was the result of negligence. The liability space from which one can recover[161] is typically, themselves, other parties, or nobody.[162] 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.[163][96][164]

As it is generally probable and 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[18][19] of precedent in negligence doctrine in addition to posing difficult policy and engineering challenges. It also violates the calculus of negligence[144] because speed is an inherent factor in vehicular accidents which are a leading cause of priceless life loss[165][166][167][168][169][128] and lawsuits, and the burden of a precautions speed is radically lower than the former.[169]

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 Darwinian misfortune upon the entire class of unwarnable accidents where drivers and their passengers would not have collided into the likes of a moose,[113] livestock,[37] fallen tree, rock, jetsam, horse-drawn vehicle,[37] stalled vehicle,[170] 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 warning them it knocked down a tree in a forest with lots of trees which all eventually fall down. 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 driving services and driver-less cars[12] 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 space into act of god, government claims, strict liability, or other 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.[171] 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.[34][35] The deceleration coefficients and reactions times may change from conveyance by chariot, horse and buggy, internal combustion engine, electric motor, and by driver-less 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,[118][119] human life reaps continued benefit from the ACDA duty of which instills the necessary room to survive uninjured from such foreseeable and excusable error while adding 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[172] 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.[10] The ACDA minimum standard gives fair notice of what conduct is prohibited, and people of ordinary intelligence can apply their braking experience or the seconds of distance to stop rule to the distance they can see;[142] 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.[11]

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 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 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 autobahns.[114]

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.[96] 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 normalization of deviance and unnecessary risk, misunderstanding the purpose of the road functional classification system, underestimation of increased risk, and reclamation of commute time.[114]

One of the greatest difficulties created by such an extension of the ACDA is the frequency at which roads reduce their functional classification[114] unbeknownst to drivers who continue unaware they have lost this extended "assurance" or don't understand the difference. Such nuance in applicable jurisdictions is a prolific source of accidents.[125] 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 signs communicating "limited sight distance," "hill blocks view," "crossroad ahead," and "freeway ends."[173] 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.[114]

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 judicial circuits.[10][47][105][174][175] Primitive patchwork governance over a prominent interstate commercial subject, in a modern era where citizens quickly and more frequently travel father than ever before, creates problems for modern driver-less cars which are programmed, distributed, sold, and traded at national levels.[12][104][140] As opposed to a strict standard of care,[176][80][81][177] delegation of such standard to a jury[178] assumes the representativeness heuristic[179] 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,[81] which works against the utility of the law by making it arbitrarily vague.[80][81] 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.[165][166][128][180] While group polarization towards safety has shifted the criminal blood alcohol threshold below levels for which the risk is statistically marginal,[6][181] the tolerance for speeding—of which each speed unit increment carries an equatable risk relative to BAC[6]—remains relatively neglected. Speed is responsible for more crashes and economic loss than is alcohol.[165] The discrepancy may be partly explained by powerful special interest groups that are lobbying against drunk driving and for loser speed regulation.[182]


Case 1: Safe speed as a function of forward line-of-sight

Free body
Forces on a vehicle skidding down a grade of angle θ.

Case 5: Safe speed as a function of critical speed

Free body
Forces on a vehicle skidding down a grade of angle θ.

Seconds of distance to stop rule

Tables of reference constants and safe speeds

Reference constants

Table of tire speed ratings

Safe speeds

Table of critical speeds

Table of detection thresholds

See also


  1. ^ For this reason, full 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.
  2. ^ 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 inferences from insufficient, distracting, or illusory information—it is especially important to foresee such hazard at intersections.
  3. ^ 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, . Given a vehicle of size and distance , the visual angle is: . Its derivative with respect to distance is . An approaching vehicle of constant velocity will decrease the distance at rate . 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: . It follows that . Hence, an approaching vehicle's looming motion is not perceivable until , where the S2/4 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 22/15 to convert MPH to ft/s or 5/18 to convert km/h to m/s or π/180 to convert deg to requisite rad). Read more about this topic
  4. ^ 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 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.
  5. ^ In most jurisdictions, judicial notice shall be taken of the 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.
    For example, using the and values that produced Code of Virginia § 46.2-880 Tables of speed and stopping distances, one simply obtains the same velocities that produced the stopping distance in the statute: Metric (SI) – Speed in km/h from distance in meters:
    US customary – Speed in MPH from distance in feet:
  6. ^ 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/s2 will produce a safe speed in terms of feet/second. To convert to miles per hour, multiply by 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 18/5 (or 3.6) factor.


  1. ^ a b c d e f g "Section 2 – Driving Safely" (PDF). Commercial Driver License Manual 2005. United States Department of Transportation. July 2014. pp. 2–15, 2–19, 2–26, 13–1. [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.
  2. ^ a b c Lawyers Cooperative Publishing. New York Jurisprudence. Automobiles and Other Vehicles. Miamisburg, OH: LEXIS Publishing. p. § 720. OCLC 321177421. 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.
  3. ^ a b c d Leibowitz, Herschel W.; Owens, D. Alfred; Tyrrell, Richard A. (1998). "The assured clear distance ahead rule: implications for nighttime traffic safety and the law". Accident Analysis & Prevention. 30 (1): 93–99. doi:10.1016/S0001-4575(97)00067-5. PMID 9542549. 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.
  4. ^ a b c James O. Pearson (2009). "Automobiles: sudden emergency as exception to rule requiring motorist to maintain ability to stop within assured clear distance ahead". American Law Reports--Annotated, 3rd Series. 75. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 327.
  5. ^ a b c Newton v. Stebbins, 51 U.S. 586, 51 United States Reports 586 (Supreme Court of the United States December 1850) ("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.").
  6. ^ a b c C.N. Kloeden; A.J. McLean; V.M. Moore; G. Ponte. "Travelling Speed and the Risk of Crash Involvement" (PDF). NHMRC Road Accident Research Unit, The University of Adelaide. p. 54. 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...
  7. ^ Benjamin Preston (January 8, 2016). "Insurers Brace for a Self-Driving Future (and a Fading Need for Insurance)". The New York Times. p. B3.
  8. ^ Murray Carl Lertzman (1954). "The Assured Clear Distance Ahead Rule in Ohio". Case Western Reserve Law Review. 5 (1): 77–83. 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
  9. ^ a b c Connally v. General Construction Co., 269 United States Reports 385, 391 (Supreme Court of the United States January 4, 1926) ("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.").
  10. ^ a b c State of Montana, v. Rudy Stanko, 1998 MT 321, HN 30 (Supreme Court of Montana 23 December 1998) ("...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.").
  11. ^ a b c d Jim Robbins (December 25, 1998). "Montana's Speed Limit of ?? M.P.H. Is Overturned as Too Vague". The New York Times. 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.
  12. ^ a b c d e f Le Vine, Scott; Liu, Xiaobo; Zheng, Fangfang; Polak, John (2016-01-01). "Automated cars: Queue discharge at signalized intersections with 'Assured-Clear-Distance-Ahead' driving strategies". Transportation Research Part C: Emerging Technologies. 62: 35–54. doi:10.1016/j.trc.2015.11.005.
  13. ^ a b c d e f g h i Reaugh v. Cudahy Packing Co., 189 Cal. 335, 189 Official California Reports 335 (Supreme Court of California July 27, 1922) ("[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 Official Reports Opinions Online
  14. ^ a b c Morris v. Jenrette Transport Co., 235 N.C. 568 (Supreme Court of North Carolina May 21, 1952) ("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." 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").
  15. ^ a b c d Allin v. Snavely, 100 Cal. App. 2d 411, 100 Official California Appellate Reports, 2nd Series 411 (California Court of Appeal November 14, 1950) (""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])").
  16. ^ a b c d e Errol R. Hoffmann; Rudolf G. Mortimer (July 1996). "Scaling of relative velocity between vehicles". Accident Analysis & Prevention. 28 (4): 415–421. doi:10.1016/0001-4575(96)00005-X. ISSN 0001-4575. 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
  17. ^ a b c d e Michael E. Maddox; Aaron Kiefer (September 2012). "Looming Threshold Limits and Their Use in Forensic Practice". Proceedings of the Human Factors and Ergonomics Society Annual Meeting. 50 (1): 700–704. doi:10.1177/1071181312561146. 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...
  18. ^ a b c d The Batavier, 40 English Reports in Law and Equity 19–27, 25 (Great Britain. Courts.; Great Britain. Parliament. House of Lords.; Great Britain. Privy Council. Judicial Committee July 14, 1854) ("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 ... See more English Reports in Law and Equity").
  19. ^ a b c The Europa, 2 English Reports in Law and Equity 557–564, 564 (Great Britain. Courts.; Great Britain. Parliament. House of Lords.; Great Britain. Privy Council. Judicial Committee June 11, 1850) ("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. See more English Reports in Law and Equity").
  20. ^ a b The Colorado, 91 U.S. 692, 91 United States Reports 692 (Supreme Court of the United States October 1875) ("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.").
  21. ^ a b c Lauson v. Town of Fond du Lac, 141 Wis. 57, 123 N. W. 629, 25 L. R. A. (N. S.) 40., 141 Wis. 57 (Wisconsin Supreme Court 1909) ("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").
  22. ^ a b Garner v. Maxwell, 360 S.W.2d 64, 360 S.W.2d 64 (Court of Appeals of Tennessee December 20, 1961) ("What is known as the "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.").
  23. ^ "International Regulations for Preventing Collisions at Sea" (PDF). International Maritime Organization (IMO), United Nations. October 20, 1972. Archived from the original (PDF) on November 7, 2012. Part B, Section I, Rule 6: Safe speed...Every vessel shall at all times proceed at a safe speed so that she can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions...See International Regulations for Preventing Collisions at Sea, 33 USC 1602: International Regulations, and Executive Order 11964
  24. ^ "Revised Statutes (1878), Title XLVIII (48), Chapter 5: Navigation, Section 4233, rules for preventing collisions". Congress of the United States. 1878. 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
  25. ^ a b The Nacoochee v. Moseley, 137 U.S. 330, 137 United States Reports 330 (Supreme Court of the United States December 8, 1890) ("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.").
  26. ^ a b Curtis v. Hubbel, 42 Ohio App. 520, 182 N. E. 589, 42 Ohio App. 520 (Court of Appeals of Ohio May 31, 1932) ("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.").
  27. ^ a b Lindquist v. Thierman, 216 Iowa 170, 216 Iowa 170 (Supreme Court of Iowa May 15, 1933) ("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.").
  28. ^ "Ohio General Code, Section 12603". July 21, 1929. 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."
  29. ^ "Iowa General Code, Section 5029 (1931)". 1931. 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.
  30. ^ McCool v. Smith, 66 United States Reports 459, 469 (Supreme Court of the United States 1861) ("It is a sound rule, that whenever our Legislature use a term without defining it, which is well known in the 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 English law.'").
  31. ^ Shapiro v. United States, 335 United States Reports 1, 16 (Supreme Court of the United States 1941) ("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."").
  32. ^ "Revised Statutes (1878), Title I General Provisions, Chapter 1, Section 3: Vessel". Congress of the United States. 1878. 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.
  33. ^ "Revised Statutes (1878), Title I General Provisions, Chapter 1, Section 4: Vehicle". Congress of the United States. 1878. 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.
  34. ^ a b Richard M. Nixon (October 1936). "Changing Rules of Liability in Automobile Accident Litigation". Law and Contemporary Problems. 3 (4): 476–490. doi:10.2307/1189341. ISSN 1945-2322. JSTOR 1189341. 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.
  35. ^ a b c Cook v. Miller, 175 Cal. 497, 175 Official California Reports 497 (Supreme Court of California June 19, 1917) ("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.").
  36. ^ "California Vehicle Code §21050". State of California. 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
  37. ^ a b c d e f "California Vehicle Code §21759". State of California. 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.
  38. ^ "California Vehicle Code §21200". State of California. 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
  39. ^ Leyden Street remains unchanged since 1620
  40. ^ Pennsylvania R. Co. v. Huss, 96 Ind. App. 71, 180 N. E. 919, 96 Indiana Appellate Reports 71 (Court of Appeals of Indiana May 6, 1932) ("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").
  41. ^ Fisher v. O'Brien, 99 Kan. 621, 192 Pac. 317, L.R.A. 1917F, 610 (1917).
  42. ^ Demerest v. Travelers Insurance Company, 234 La. 1048, 234 La. 1040 (Supreme Court of Louisiana April 21, 1958) ("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.").
  43. ^ Carriere v. Aetna Cas. Co., 146 So.2d 451, 146 So.2d 451 (Court of Appeal of Louisiana. Fourth Circuit October 1, 1962) ("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.").
  44. ^ Spencer v. Taylor, 219 Mich. 110, 188 N.W. 461 (1922), 219 Mich. 110 (1922).
  45. ^ Gleason v. Lowe, 232 Mich. 300, 232 Mich. 300 (Supreme Court of Michigan October 1, 1925) ("...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.").
  46. ^ a b c Ruth v. Vroom, 245 Mich. 88, 222 N. W. 155, 62 A. L. R. 1528, 245 Mich. 88 (Supreme Court of Michigan December 4, 1928) ("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.").
  47. ^ a b O'Farrell v. Inzeo, 74 A.D.2d 806 (1st Dept. 1980), 74 A.D.2d 806 (New York Supreme Court, Appellate Division 1980) ("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.").
  48. ^ Blair v. Goff-Kirby Co., 49 Ohio St.2d 5, 7 (Supreme Court of Ohio December 29, 1976).
  49. ^ West Constr. Co. v. White, 130 Tenn. 520, 172 S.W. 301 (1914) ("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.").
  50. ^ Steele v. Fuller, 104 Vt. 303, 104 Vt. 303 (November 1932) ("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.").
  51. ^ Mann v. Reliable Transit Co., 217 Wis. 465, 259 N. W. 415, 217 Wis. 465 (Wisconsin Supreme Court 1935).
  52. ^ Satterlee v. Orange Glenn School Dist., 29 Cal.2d 581, 29 Official California Reports, 2nd Series 581 (California Supreme Court Jan 31, 1947) (""proper conduct of a reasonable person under particular situations may become settled by judicial decision or be prescribed by statute or ordinance.""). See California Official Reports: Online Opinions
  53. ^ a b Wilding v. Norton, 156 Cal.App.2d 374, 156 Official California Appellate Reports, 2nd Series 374 (California Appellate Court December 27, 1957) ("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. See Official Reports Online").
  54. ^ a b c d Whitelaw v. McGilliard,179 Cal. 349, 179 Official California Reports 349 (Supreme Court of California December 4, 1918) ("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 Official Reports Opinions Online").
  55. ^ Lutz v. Schendel, 175 Cal. App. 2d 140, 175 Official California Appellate Reports, 2nd Series 140 (California Appellate Court Nov 6, 1959) (""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 California Official Reports: Online Opinions
  56. ^ "Code § 321.285 Speed restrictions". The State of Iowa. Retrieved August 6, 2013. 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.
  57. ^ "§ 257.627 Speed limitations". The State of Michigan. Retrieved August 6, 2013. § 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.
  58. ^ "Revised Code § 4511.21(A) Speed limits - assured clear distance". The State of Ohio. Retrieved August 6, 2013. § 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.
  59. ^ "Oklahoma Statutes § 47-11-801". The State of Oklahoma. Retrieved August 6, 2013. 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.
  60. ^ "75 Pa. Cons. Stat. § 3361. Driving vehicle at safe speed". The State of Pennsylvania. Retrieved August 6, 2013. 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.
  61. ^ "Transportation Code, Title 7, Ch. 545, §545.062(a)". State of Texas. Retrieved 25 March 2018. 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.
  62. ^ "Member States". International Maritime Organization (IMO), United Nations. Retrieved 3 July 2018. Members of IMO are governed by International Regulations for Preventing Collisions at Sea—Part B, Section I, Rule 6: Safe speed
  63. ^ "Boating Safety". Archived from the original on 2013-09-28. Retrieved 2013-08-27. 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.
  64. ^ "HAWAII ADMINISTRATIVE RULES, TITLE 13, DEPARTMENT OF LAND AND NATURAL RESOURCES, SUBTITLE 11, OCEAN RECREATION AND COASTAL AREAS, PART II, BOATING, CHAPTER 244" (PDF). The State of Hawaii. 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.
  65. ^ "Illinois Compiled Statutes, Ch. 625, Boat Registration and Safety Act. Sec. 5-1". The State of Illinois. 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.
  66. ^ "Louisiana Laws - RS 34:851.4 — Careless operation". The State of Louisiana. 2006. Any person who shall operate any watercraft ... 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 shall be guilty of the crime of careless operation...Also See LA. Dept. of Wildlife and Fisheries regulations
  67. ^ Torrez v. Willett, 366 Mich. 465, 366 Mich. 465 (Supreme Court of Michigan May 18, 1962) ("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."").
  68. ^ "§ 23-2-523(4). Prohibited operation and mooring -- enforcement". The State of Montana. Retrieved August 6, 2013. § 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.
  69. ^ "Oregon Revised Statues § 830.315 - Reckless operation speed". § 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.
  70. ^ "Boating Safety: Operate at a Safe Speed". The State of Texas. 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.
  71. ^ "Article 7, Chapter 20 of the Official Code of West Virginia" (PDF).
  72. ^ a b "Visual Search: How Well Can You Stop?". Driver Handbook (PDF). State of California: Department of Motor Vehicles. 2015. p. 39. 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.
  73. ^ a b Alaska Driver Manual (PDF). State of Alaska. p. 28. 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
  74. ^ a b "North Carolina Driver's Handbook" (PDF). N.C. Division of Motor Vehicles. pp. 51, 66. Archived from the original (PDF) on 2016-03-04. Retrieved 2016-02-25. 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
  75. ^ Driver's Manual (PDF). Oklahoma Department of Public Safety. pp. 8–2.
  76. ^ Driver's Manual (PDF). Iowa Department of Transportation. p. 39.
  77. ^ Road Users Manual (PDF). Newfoundland and Labrador, Canada. p. 49.
  78. ^ Road Users Manual (PDF). Prince Edward Island, Canada. p. 88.
  79. ^ "49 CFR 392.14 - Hazardous conditions; extreme caution". US Code of Federal Regulations. 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.
  80. ^ a b c d e Baltimore & Ohio R. Co. v. Goodman, 275 U.S. 66, 275 United States Reports 66 (Supreme Court of the United States October 31, 1927) ("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.").
  81. ^ a b c d e f g Oliver Wendell Holmes, Jr. (1881). "Lecture III—D. Liability for unintended Harm is determined by what would be Blameworthy in Average man". The Common Law. Little, Brown and Company. p. 108,122,123. 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.
  82. ^ "Federal Motor Vehicle Safety Standards; Event Data Recorders". Federal Register. December 12, 2012.
  83. ^ "Event Data Recorder Supported Vehicles" (PDF). Rimkus Consulting Group, Inc. July 2015.
  84. ^ a b c "Here's why lawyers are 'salivating' over self-driving cars". Business Insider Inc. December 22, 2015. 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."
  85. ^ "Urban Street Design Guide". National Association of City Transportation Officials. 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.
  86. ^ "Caltrans Backs Innovative Street Design Guides to Promote Biking and Walking". California Department of Transportation. April 11, 2014. 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.
  87. ^ Eloisa Raynault; Ed Christopher (May 2013). "How Does Transportation Affect Public Health? (FHWA-HRT-13-004)". Public Roads. 76 (6).
  88. ^ "CDC Transportation Recommendations". Atlanta, GA: Centers for Disease Control and Prevention. 2018-02-07. 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.
  89. ^ "Smart Growth and Transportation". Washington, DC: United States Environmental Protection Agency. 2013-04-26. 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.
  90. ^ "Transportation". Smart Growth America. 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.
  91. ^ "More Choices, Less Traffic". National Resource Defense Council. 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.
  92. ^ "Transportation Choices for Sustainable Communities". 2014-01-17.
  93. ^ "What is universal access?". 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.
  94. ^ "Blunders in Traffic Law and Enforcement". Bicycle Blunders and Smarter Solutions. LAB Reform.
  95. ^ "Assured Clear Distance Ahead and Vision Zero". BikeWalk NC. October 2015.
  96. ^ a b c William Kenworthy (January 1, 2000). Killer Roads: From Crash to Verdict (2nd ed.). Lexis Law Pub. ISBN 978-0327100164.
  97. ^ Van Praag v. Gale, 107 Cal 438 (Supreme Court of California June 6, 1895) ("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.").
  98. ^ Doyle v. Eschen, 5 Cal.App 55 (California Court of Appeal February 21, 1907) ("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.").
  99. ^ Malinson v. Black, 83 Cal.App.2d 375, 377-378 (California Court of Appeal January 27, 1948) ("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.").
  100. ^ ""Martin-Quinn" measures of judicial ideology". University of California.
  101. ^ Andrew Cabasso (September 3, 2015). "Vehicles Lawyers Should Not Drive". 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.
  102. ^ "Influence & Lobbying: Transportation". Washington, DC: Center for Responsive Politics. 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.
  103. ^ United States v. National City Lines, Inc., et al, 186 F.2d 562 (United States Court of Appeals for the Seventh Circuit January 3, 1951) ("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, Standard, Phillips, General Motors and 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 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...").
  104. ^ a b R. J. H. (January 1937). "The Uniform Motor Vehicle Act in Virginia". Virginia Law Review. 23 (3): 351–358. doi:10.2307/1067282. JSTOR 1067282. 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 1920's 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...
  105. ^ a b Stuart Silverstein (November 20, 2012). "Traffic Deaths: A Surprising Dimension of the Red State-Blue State Divide". FairWarning. blue states tend to adopt stronger safety laws, while red states opt for looser regulation
  106. ^ a b c d e f g A Policy on Geometric Design of Highways and Streets (6th ed.). American Association of State Highway and Transportation Officials. 2011. ISBN 978-1560515081.
  107. ^ a b c d e "Tables of speed and stopping distances". The State of Virginia.
  108. ^ a b Cannon v. Kemper, 23 Cal. App. 2d 239, 23 Official California Appellate Reports, 2nd Series 239 (California Appellate Court October 21, 1937). 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 California Official Reports: Online Opinions
  109. ^ Hatzakorzian v. Rucker-Fuller Desk Co., 197 Cal. 82, 197 Official California Reports 82 (Supreme Court of California September 21, 1925) (""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.."").
  110. ^ a b c Bove v. Beckman, 236 Cal. App. 2d 555, 236 Official California Appellate Reports, 2nd Series 555 (California Appellate Court Aug 16, 1965) (""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 California Official Reports: Online Opinions
  111. ^ Falasco v. Hulen, 6 Cal. App. 2d 224, 6 Official California Appellate Reports, 2nd Series 224 (California Appellate Court April 17, 1935) (""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 California Official Reports: Online Opinions
  112. ^ a b c d Riggs v. Gasser Motors, 22 Cal. App. 2d 636, 22 Official California Appellate Reports, 2nd Series 636 (California Court of Appeal September 25, 1937) (""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 basic always governing.""). See Official Reports Opinions Online
  113. ^ a b c d Meisingset, Erling L; Loe, Leif E; Brekkum, Øystein; Mysterud, Atle (2014). "Targeting mitigation efforts: The role of speed limit and road edge clearance for deer–vehicle collisions". The Journal of Wildlife Management. 78 (4): 679–688. doi:10.1002/jwmg.712. speed limit reduction and road edge clearance are both powerful mitigation tools to reduce the number of Deer–vehicle collisions.
  114. ^ a b c d e "Speeding Counts...on all roads!" (PDF). Federal Highway Administration (FHWA). November 2000. 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.
  115. ^ a b c Leeper v. Nelson, 139 Cal. App. 2d 65, 139 Official California Appellate Reports, 2nd Series 65 (California Court of Appeal Feb 6, 1956) (""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 Huetter v. Andrews, 91 Cal. App. 2d 142, Berlin v. Violett, 129 Cal.App. 337, Reaugh v. Cudahy Packing Co., 189 Cal. 335, and Official Reports Opinions Online
  116. ^ a b c d McKernan, Megan (13 May 2015). "AAA Tests Shine High-Beam on Headlight Limitations". AAA Automotive Research Center. Retrieved 3 July 2018. AAA's test results suggest that 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 HID and LED 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.
  117. ^ a b Varghese, Cherian; Shankar, Umesh (May 2007). "Passenger Vehicle Occupant Fatalities by Day and Night – A Contrast". Washington, DC: National Highway Traffic Safety Administration. National Center for Statistics and Analysis. 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.
  118. ^ a b c d e Malinson v. Black, 83 Cal. App. 2d 377, 83 Official California Appellate Reports, Second Series 377 (California Appellate Court January 27, 1948) ("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. See Official Reports Online.").
  119. ^ a b c d e Nevis v. Pacific Gas & Electric Co., 43 Cal.2d 626, 43 Official California Reports, Second Series 626 (Supreme Court of California November 9, 1954) ("Nonnegligent ignorance of the facts which bring a regulation into operation will support a finding that violation thereof is civilly excusable. See Official Reports Online").
  120. ^ Lappin JS, Tadin D, Nyquist JB, Corn AL (January 2009). "Spatial and temporal limits of motion perception across variations in speed, eccentricity, and low vision". Journal of Vision. 9 (30): 30.1–14. doi:10.1167/9.1.30. PMID 19271900. Displacement thresholds for peripheral motion were affected by acuity limits for speeds below 0.5 degrees/s. [0.0087 radians/s]
  121. ^ "California Vehicle Code §275(a)". The State of California. "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.
  122. ^ "California Vehicle Code §21950(a)&(c)". The State of California. 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.
  123. ^ "California Vehicle Code §231.6(a)". The State of California. 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.
  124. ^ a b c d e f g h J. Stannard Baker (1963). Traffic Accident Investigator's Manual for Police (2 ed.). The Traffic Institute, Northwestern University. pp. 43–48. LCCN 62-20895.
  125. ^ a b c d Grasso v. Cunial, 106 Cal. App. 2d 294, 106 California Official Reports, 2nd Series 294 (California Court of Appeal August 27, 1951) ("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 Official Reports Opinions Online").
  126. ^ a b c d Page v. Mazzei, 213 Cal. 644, 213 Official California Reports 644 (Supreme Court of California 21 September 1931) ("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 Official Reports Opinions Online").
  127. ^ Fitts v. Marquis, 127 Me. 75, 127 Maine Reporter 75 (Supreme Judicial Court of Maine March 15, 1928) ("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.").
  128. ^ a b c d e Raymond S. Nickerson; The National Research Council (September 15, 1995). "9". Emerging Needs and Opportunities for Human Factors Research. The National Academies Press. doi:10.17226/4940. ISBN 978-0309052764. 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.
  129. ^ a b Hershel Weinberger (19 February 1971). "Conjecture on the Visual Estimation of Relative Radial Motion". Nature. 229 (5286): 562. doi:10.1038/229562a0. PMID 4925353.
  130. ^ Joseph S. Lappin; Duje Tadin; Jeffrey B. Nyquist; Anne L. Corn (January 2009). "Spatial and temporal limits of motion perception across variations in speed, eccentricity, and low vision". Journal of Vision. 9 (30): 30. doi:10.1167/9.1.30. PMID 19271900. Displacement thresholds for peripheral motion were affected by acuity limits for speeds below 0.5 degrees/s.
  131. ^ Paul R. Schrater; David C. Knill; Eero P. Simoncelli (12 April 2001). "Perceiving visual expansion without optic flow". Nature. 410 (6830): 816–819. doi:10.1038/35071075. PMID 11298449. 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.
  132. ^ Melvyn A. Goodale (1 July 2011). "Transforming vision into action". Vision Research. 51 (13): 1567–1587. doi:10.1016/j.visres.2010.07.027. ISSN 0042-6989. PMID 20691202.
  133. ^ "Section 13: On-Road Driving". California Commercial Driver Handbook (2014-2015) (PDF). California Department of Motor Vehicles. 2015. pp. 2–19, 13–2. [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.
  134. ^ a b c "Title 23, Code of Federal Regulations, Part 655.603". US Government Publishing Office. 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.
  135. ^ "3B.16.10". California MUTCD 2014. California Department of Transportation. p. 681. 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.
  136. ^ "405.1". California Highway Design Manual. California Department of Transportation. 2012. pp. 400–14. 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.
  137. ^ a b A Policy on Geometric Design of Rural Highways. American Association of State Highway and Traffic Officials. 1969. p. 394. 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.
  138. ^ a b c d e "Geometric Design And Structure Standards" (PDF). Highway Design Manual. California Department of Transportation. pp. 200–1, 200–2, 200–3, 200–4, 200–7, 200–10, 200–11, 200–20.
  139. ^ Geoff Manaugh (November 15, 2015). "Sightlines/The Dream Life of Driverless Cars". The New York Times. p. MM68. 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.
  140. ^ a b Matt Richtel; Conor Dougherty (September 2, 2015). "Google's Driverless Cars Run Into Problem: Cars With Drivers". The New York Times. p. A1. 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.
  141. ^ a b Fox v. City and County of San Francisco, 47 Cal.App.3d 164, 47 Official California Appellate Reports, 3rd Series 164 (California Appellate Court April 14, 1975) ("drivers with mental disabilities are required to exercise the ordinary care required of an adult without such disability. See Official Reports Online.").
  142. ^ a b c d James J. Gibson; Laurence E. Crooks (July 1938). "A Theoretical Field-Analysis of Automobile-Driving". The American Journal of Psychology. 51 (3): 453–471. doi:10.2307/1416145. ISSN 0002-9556. JSTOR 1416145. OCLC 473102987.
  143. ^ "Common Core State Standard for Mathematics" (PDF). Common Core State Standards Initiative. p. 27. See 4th grade math level
  144. ^ a b United States v. Carroll Towing Co., 159 Federal Reporter, Second Series 169, 173 (United States Court of Appeals for the Second Circuit January 9, 1947) ("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. See ruling here").
  145. ^ a b Taoka, George T. (March 1989). "Brake Reaction Times of Unalerted Drivers" (PDF). ITE Journal. 59 (3): 19–21.
  146. ^ a b Paul L. Olson; Michael Sivak (February 1986). "Perception-response time to unexpected roadway hazards" (PDF). Human Factors. 28 (1): 91–96. doi:10.1177/001872088602800110. PMID 3710489. 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.
  147. ^ Booth v. Columbia Casualty Company, 227 La. 932 (Supreme Court of Louisiana April 25, 1955) ("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.").
  148. ^ a b c d John C. Glennon; Paul F. Hill (2004). Roadway Safety and Tort Liability (2 ed.). Lawyers & Judges Publishing Company, Inc. p. 293. ISBN 9781930056947.
  149. ^ "Critical Speed Calculator". The CAD Zone. Inc. 2015.
  150. ^ State of Montana v. Rudy Stanko (Supreme Court of Montana 23 December 1998) ("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."). Text
  151. ^ "Speed Concepts: Informational Guide". US Department of Transportation. 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.
  152. ^ a b "Title 23 Code of Federal Regulations, Part 625.4". U.S. Government Printing Office.
  153. ^ a b c "2009 Edition Chapter 2B. Regulatory Signs, Barricades, and Gates". Manual on Uniform Traffic Control Devices (MUTCD). Federal Highway Administration. [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
  154. ^ a b Maev Kennedy (September 6, 2013). "'All you could hear was cars crashing': 120-car pile-up on Sheppey bridge". The Guardian. 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."
  155. ^ Reinders v. Olsen, 60 Cal. App. 764, 60 California Appellate Reports 764 (California Appellate Court February 13, 1923) ("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 Official Reports Opinions").
  156. ^ Iain A. McCormick; Frank H. Walkey; Dianne E. Green (June 1986). "Comparative perceptions of driver ability–A confirmation and expansion". Accident Analysis & Prevention. 18 (3): 205–208. doi:10.1016/0001-4575(86)90004-7. ISSN 0001-4575. a substantial majority of drivers, up to 80%, would rate themselves above average on a number of important characteristics
  157. ^ "Speed Concepts: Informational Guide". US Department of Transportation. Inferred design speed – the maximum speed for which all critical design-speed-related criteria are met at a particular location.
  158. ^ Kahneman, Daniel (December 2003). "Maps of Bounded Rationality: Psychology for Behavioral Economics". American Economic Review. 93 (5): 1449–1475. CiteSeerX doi:10.1257/000282803322655392. ISSN 0002-8282.
  159. ^ "National Committee on Uniform Traffic Control Devices (NCUTCD)". Archived from the original on 2016-03-05. Retrieved 2016-02-26.
  160. ^ "61-8-303(1)(b)&(3) - Speed restrictions". Montana Code Annotated. State of Montana. Retrieved 4 July 2018. 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.
  161. ^ "CA Civil Code §3333". The State of California. Archived from the original on 2016-01-15. Retrieved 2015-12-15. 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.
  162. ^ Cordova v. Ford, 46 Cal. App. 2d 180, 46 California Appellate Reports, Second Series 180 (California Appellate Court 7 November 1966) (""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 Official Reports Opinions Online
  163. ^ Peri v. L. A. Junction Railway, 22 Cal.2d 111, 22 Official California Reports, Second Series 111 (Supreme Court of California 3 May 1943) ("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 Official Reports Opinions Online").
  164. ^ Chowdhury v. City of Los Angeles, 38 Cal.App.4th 1187, 38 Official California Appellate Reports, 4th Series 1187 (California Appellate Court September 5, 1995) (""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 Official Reports Opinions Online").
  165. ^ a b c National Center for Statistics and Analysis (July 2015). "Overview: 2013 data. (Traffic Safety Facts. Report No. DOT HS 812 169)" (PDF). Washington, DC: National Highway Traffic Safety Administration. 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.
  166. ^ a b Leighton Walter Kille (October 5, 2014). "Transportation safety over time: Cars, planes, trains, walking, cycling". Harvard Kennedy School's Shorenstein Center and the Carnegie-Knight Initiative. 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%."
  167. ^ Herbert William Heinrich (1931). Industrial accident prevention: a scientific approach. McGraw-Hill insurance series. McGraw-Hill. LCCN 31004075. OCLC 571338960. for every accident that causes a major injury, there are 29 accidents that cause minor injuries and 300 accidents that cause no injuries
  168. ^ Binyamin Appelbaum (February 16, 2011). "As U.S. Agencies Put More Value on a Life, Businesses Fret". The New York Times. The Environmental Protection Agency set the value of a life at $9.1 million...
  169. ^ a b Frank Partnoy (July 21, 2012). "The Cost of a Human Life, Statistically Speaking". The Globalist. 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...
  170. ^ Self v. State Farm Mutual Automobile Insurance Co., 183 So. 2d 68, 183 So.2d 68 (Court of Appeal of Louisiana, Third Circuit February 15, 1966) ("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.").
  171. ^ "Connected Vehicle Pilot Program". US Department of Transportation. 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.
  172. ^ Sam Peltzman (August 1975). "The Effects of Automobile Safety Regulation". Journal of Political Economy. 83 (4): 677–726. doi:10.1086/260352. JSTOR 1830396.
  173. ^ Manual on Uniform Traffic Control Devices for Streets and Highways (2009 ed.). US Dept. of Transportation, Federal Highway Administration. 2012. pp. 117, 119, 127. ISBN 978-1598045369. 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)
  174. ^ National Center for Statistics and Analysis (September 2015). "State traffic data: 2013 data (Traffic Safety Facts. Report No. DOT HS 812 196)" (PDF). Washington, DC: National Highway Traffic Safety Administration. 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.
  175. ^ "General statistics". Insurance Institute for Highway Safety (IIHS). 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.
  176. ^ Herbert v. Southern Pac. Co., 121 Cal. 227, 121 Official California Reports 227 (Supreme Court of California June 20, 1898) ("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.").
  177. ^ Healthcare at Home Limited v. The Common Services Agency, [2014] UKSC 49 (Supreme Court of the United Kingdom 30 July 2014) ("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 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."). Text
  178. ^ Newton N. Minow; Fred H. Cate (Winter 1991). "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". American University Law Review. 40: 631. 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.
  179. ^ Amos Tversky; Daniel Kahneman (August 1971). "Belief in the law of small numbers". Psychological Bulletin. 76 (2): 105–110. CiteSeerX doi:10.1037/h0031322. 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.
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  182. ^ Aaron Claverie (August 13, 2015). "TEMECULA: Inquiries prompt new speed survey". The Press Enterprise. 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.
  183. ^ Lora Warshawsky-Livne; David Shinar (Spring 2000). "Effects of uncertainty, transmission type, driver age and gender on brake reaction and movement time". Journal of Safety Research. 33 (1): 117–128. doi:10.1016/S0022-4375(02)00006-3. ISSN 0022-4375. 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).
  184. ^ FC Donders (January 1969). "On the speed of mental processes". Acta Psychologica. 30: 412–31. doi:10.1016/0001-6918(69)90065-1. ISSN 0001-6918. OCLC 1447968. PMID 5811531.
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  189. ^ "CAMUTCD". California Department of Transportation. p. 984. a bicyclist riding a bicycle 6 feet long to clear the last conflicting lane at a speed of 14.7 feet/sec
  190. ^ "European Tyre and Rim Technical Organisation Standards Manual 2010 G6" (PDF). The European Tire and Rim Technical Organization.
  191. ^ "Urban Street Design Guide: Lane Width". National Association of City Transportation Officials. as the width of the lane increased, the speed of the roadway increased
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Further reading: tertiary sources

ACDA related law reviews

  • James O. Pearson (2009). "Automobiles: sudden emergency as exception to rule requiring motorist to maintain ability to stop within assured clear distance ahead". American Law Reports--Annotated, 3rd Series. 75. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 327.
  • W. R. Habeeb (2010). "Liability for motor vehicle accident where vision of driver is obscured by smoke, dust, atmospheric condition, or unclean windshield". American Law Reports--Annotated, 2nd Series. 42. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 13.
  • Wade R. Habeeb (2009). "Liability or recovery in automobile negligence action as affected by driver's being blinded by lights other than those of a motor vehicle". American Law Reports--Annotated, 3rd Series. 64. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 760.
  • Wade R. Habeeb (c. 2009). "Liability or recovery in automobile negligence action as affected by driver's being blinded by lights of motor vehicle". American Law Reports--Annotated, 3rd Series. 64. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 551.
  • L. S. Tellier (2011). "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". American Law Reports--Annotated, 2nd Series. 59. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 1202.
  • ""Assured clear distance" statute or rule as applied at hill or curve". American Law Reports--Annotated. 133. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 967.
  • "Application of "assured clear distance ahead" or "radius of lights" doctrine to accident involving pedestrian crossing the street or highway". American Law Reports--Annotated, 2nd Series. 31. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 1424.
  • "Driving automobile at speed which prevents stopping within range of vision as negligence". American Law Reports--Annotated, 2nd Series. 44;58;87;97. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 1403;1493;900;546.
  • "Driver's failure to maintain proper distance from motor vehicle ahead". American Law Reports--Annotated, 2nd Series. 85. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 613.
  • "Motor vehicle operator's liability for accident occurring while driving with vision obscured by smoke or steam". American Law Reports--Annotated, 4th Series. 32. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 933.
  • "Duty and liability of vehicle driver blinded by glare of lights". American Law Reports--Annotated, 2nd Series. 22. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 292.
  • "Liability for killing or injuring, by motor vehicle, livestock or fowl on highway". American Law Reports--Annotated, 4th Series. 55. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 822.
  • R. J. H. (January 1937). "The Uniform Motor Vehicle Act in Virginia". Virginia Law Review. 23 (3): 351–358. doi:10.2307/1067282. JSTOR 1067282.
  • D. M. Postlewaite (1935). "Negligence -- Doctrine of Assured Clear Distance Ahead -- Statute as Subjective Test". Law Journal of the Student Bar Association of the Ohio State University. 1 (3): 284–287. hdl:1811/72043. ISSN 0048-1572.
  • Thomas Stanton (July 1935). "Negligence and Contributory Negligence Per Se: The "Range of Vision" and "Blinding Lights" Rules in Automobile Accident Cases". California Law Review. 23 (5): 498–506. doi:10.2307/3476106. JSTOR 3476106.
  • Myron L. Garon (Autumn 1952). "Recent Developments in California's Last Clear Chance Doctrine". California Law Review. 40 (3): 404–411. doi:10.2307/3477930. JSTOR 3477930.
  • Murray Carl Lertzman (1954). "The Assured Clear Distance Ahead Rule in Ohio". Case Western Reserve Law Review. 5 (1): 77–83.
  • Herbert A. Bernhard (December 1956). "Negligence: Breach of Duty: Assured Clear Distance Ahead Doctrine". Michigan Law Review. 55 (2): 299–301. doi:10.2307/1285419. JSTOR 1285419.
  • Winston R. Day (December 1969). "Assured Clear Distance Doctrine in Louisiana". Louisiana Law Review. 30 (1): 129–139.
  • Alfred A. Sniadowski; John De Mots; Charles S. Reddy; Frank E. Bright (1938). "Recent Decisions". Notre Dame Law Review. 13 (4).
  • Richard M. Nixon (October 1936). "Changing Rules of Liability in Automobile Accident Litigation". Law and Contemporary Problems. 3 (4): 476–490. doi:10.2307/1189341. ISSN 0023-9186. JSTOR 1189341.

Other printed resources

Web resources


ACDA may refer to:

Allegheny County District Attorney

American Choral Directors Association, a non-profit organization

Arms Control and Disarmament Agency, an independent agency

Assured Clear Distance Ahead, a fundamental driving principle

Thomas Acda (born March 6, 1967), television actor

Braking distance

Braking distance refers to the distance a vehicle will travel from the point when its brakes are fully applied to when it comes to a complete stop. It is primarily affected by the original speed of the vehicle and the coefficient of friction between the tires and the road surface, and negligibly by the tires' rolling resistance and vehicle's air drag. The type of brake system in use only affects trucks and large mass vehicles, which cannot supply enough force to match the static frictional force.The braking distance is one of two principal components of the total stopping distance. The other component is the reaction distance, which is the product of the speed and the perception-reaction time of the driver/rider. A perception-reaction time of 1.5 seconds, and a coefficient of kinetic friction of 0.7 are standard for the purpose of determining a bare baseline for accident reconstruction and judicial notice; most people can stop slightly sooner under ideal conditions.

Braking distance is not to be confused with stopping sight distance. The latter is a road alignment visibility standard that provides motorists driving at or below the design speed an assured clear distance ahead (ACDA) which exceeds a safety factor distance that would be required by a slightly or nearly negligent driver to stop under a worst likely case scenario: typically slippery conditions (deceleration 0.35g) and a slow responding driver (2.5 seconds). Because the stopping sight distance far exceeds the actual stopping distance under most conditions, an otherwise capable driver who uses the full stopping sight distance, which results in injury, may be negligent for not stopping sooner.

Cycling infrastructure

Cycling infrastructure refers to all infrastructure which may be used by cyclists. This includes the same network of roads and streets used by motorists, except those roads from which cyclists have been banned (e.g., many freeways/motorways), plus additional bikeways that are not available to motor vehicles, such as bike paths, bike lanes, cycle tracks and, where permitted, sidewalks, plus amenities like bike racks for parking and specialized traffic signs and signals. Cycling modal share is strongly associated with the size of local cycling infrastructure.

The manner in which the public road network is designed, built and managed can have a significant effect on the utility and safety of cycling. The cycling network may be able to provide the users with direct, convenient routes minimizing unnecessary delay and effort in reaching their destinations. Settlements with a dense road network of interconnected streets tend to be viable utility cycling environments.

Death of Elaine Herzberg

The death of Elaine Herzberg (August 2, 1968 – March 18, 2018) was the first recorded case of a pedestrian fatality involving a self-driving (autonomous) car, following a collision that occurred late in the evening of March 18, 2018. Herzberg was pushing a bicycle across a four-lane road in Tempe, Arizona, United States, when she was struck by an Uber test vehicle, which was operating in self-drive mode with a human safety backup driver sitting in the driving seat. Following the collision, Herzberg was taken to the hospital where she died of her injuries.As a result of the fatal incident, Uber immediately suspended testing of self-driving vehicles in Arizona, where such testing had been sanctioned since August 2016. Uber also decided not to renew its permit for testing self-driving vehicles in California when it expired at the end of March 2018.Herzberg was specifically the first pedestrian death involving a self-driving car; a previous fatality, in which the driver of a semi-autonomous car was killed, had occurred almost two years prior. A Washington Post reporter compared Herzberg's fate with that of Bridget Driscoll who, in the United Kingdom in 1896, was the first pedestrian to be killed by an automobile. This incident has magnified the importance of collision avoidance systems for self-driving vehicles.

Defensive driving

The standard Safe Practices for Motor Vehicle Operations, ANSI/ASSE Z15.1, defines defensive driving skills as "driving to save lives, time, and money, in spite of the conditions around you and the actions of others." This definition is taken from the National Safety Council's Defensive Driving Course. It is a form of training for motor vehicle drivers that goes beyond mastery of the rules of the road and the basic mechanics of driving. Its aim is to reduce the risk of collision by anticipating dangerous situations, despite adverse conditions or the mistakes of others. This can be achieved through adherence to a variety of general guidelines, such as following the assured clear distance ahead and two second rules, as well as the practice of specific driving techniques. Some motorists describe defensive driving as "driving as if everyone else on the road were drunk."

Design speed

The design speed is a tool used to determine geometric features of a new road during road design. Contrary to the word's implication, a road's design speed is not necessarily its maximum safe speed; that can be higher or lower.

Geometric design of roads

The geometric design of roads is the branch of highway engineering concerned with the positioning of the physical elements of the roadway according to standards and constraints. The basic objectives in geometric design are to optimize efficiency and safety while minimizing cost and environmental damage. Geometric design also affects an emerging fifth objective called "livability," which is defined as designing roads to foster broader community goals, including providing access to employment, schools, businesses and residences, accommodate a range of travel modes such as walking, bicycling, transit, and automobiles, and minimizing fuel use, emissions and environmental damage.Geometric roadway design can be broken into three main parts: alignment, profile, and cross-section. Combined, they provide a three-dimensional layout for a roadway.

The alignment is the route of the road, defined as a series of horizontal tangents and curves.

The profile is the vertical aspect of the road, including crest and sag curves, and the straight grade lines connecting them.

The cross section shows the position and number of vehicle and bicycle lanes and sidewalks, along with their cross slope or banking. Cross sections also show drainage features, pavement structure and other items outside the category of geometric design.

Intelligent speed adaptation

Intelligent speed adaptation (ISA), also known as alerting, and intelligent authority, is any system that ensures that vehicle speed does not exceed a safe or legally enforced speed. In case of potential speeding, a human driver can be alerted, or the speed reduced automatically.

Intelligent speed adaptation uses information about the road to determine the required speed. Information can be obtained from knowledge of the vehicle position, taking into account speed limits known for the position, and by interpreting road features such as signs. ISA systems are designed to detect and alert a driver when a vehicle has entered a new speed zone, or when different speed limits are in force according to time of day and conditions. Many ISA systems also provide information about driving hazards (e.g. high pedestrian movement areas, railway crossings, schools, hospitals, etc.) and limits enforced by speed and CCTV cameras at traffic lights. The purpose of ISA is to assist the driver to maintain a safe speed.

Research has found that, in urban areas, the number of crashes causing casualties is doubled for each 5 km/h (3.1 mph) over the limit.Enforcing speed limits strictly enough to eliminate slight overspeed is difficult; it is proposed that ISA will assist with this. It is also argued that speed limits need to be properly set as those too low will equally cause issues. Drivers maintaining speeds significantly below a posted limit have been shown to have an increased accident risk compared to those nearer the limit (including those slightly over the limit).

Moving violation

A moving violation is any violation of the law committed by the driver of a vehicle while it is in motion. The term "motion" distinguishes it from other motor vehicle violations, such as paperwork violations (which include violations involving automobile insurance, registration and inspection), parking violations, or equipment violations. Moving violations often increase insurance premiums.

National cycling route network

A national cycling route network is a nationwide network of designated long-distance cycling routes found in various countries around the world for the purposes of bicycle tourism. They are often created and maintained by the government of the country, or at least with the backing or co-operation of the government of the country. Some of the routes in these national networks can be part of international long-distance cycling routes, such as the EuroVelo network of European cycling routes.

Examples of these national networks are the Dutch LF-routes, the routes of the British National Cycle Network, and the USA's United States Bicycle Route System.


Denmark: the 11 Danish National Cycle Routes

Germany: the German Cycling Network consisting of 12 so-called D-Routes

Italy: (a proposed network, BicItalia)

France: (a proposed network, Les Véloroutes et Voies Vertes de France)

The Netherlands: the 26 Dutch National Cycle Routes, the so-called LF-routes

Norway: the 10 routes of the Norwegian National Cycle Routes network

Sweden: The 15 main routes of the Sverigeleden (Sweden Route) and their branch routes

Switzerland: A network of 9 routes, the Swiss National Bike Routes

United Kingdom: the National Cycle Network, of 10 primary routes and scores of secondary routes

North America

United States Bicycle Route System

Operating speed

The operating speed of a road is the speed at which motor vehicles generally operate on that road.

The precise definition of "operating speed", however, is open to debate. Some sources, such as the AASHTO, have changed their definitions recently to match the common use of the word. In 1994, the AASHTO Green Book defined the operating speed as "the highest overall speed at which a driver can travel on a given highway

under favorable weather conditions and under prevailing traffic conditions without at any time exceeding the safe speed as determined by the design speed on a section-by-section basis," a definition which a majority of US states still use. In July 2001, however, the AASHTO revised their definition for the new edition of the Green Book and defined it as "the speed at which drivers are observed operating their vehicles during free-flow conditions."

Road slipperiness

Road slipperiness is a condition of low skid resistance due to insufficient road friction. It is a result of snow, ice, water, loose material and the texture of the road surface on the traction produced by the wheels of a vehicle.Road slipperiness can be measured either in terms of the friction between a freely-spinning wheel and the ground, or the braking distance of a braking vehicle, and is related to the coefficient of friction between the tyre and the road surface.

Public works agencies spend a sizeable portion of their budget measuring and reducing road slipperiness. Even a small increase in slipperiness of a section of road can increase the accident rate of the section of road tenfold. Maintenance activities affecting slipperiness include drainage repair, snow removal and street sweeping. More intensive measures may include grinding or milling a surface that has worn smooth, a surface treatment such as a chipseal, or overlaying a new layer of asphalt.

A specific road safety problem is split friction or μ (mu) - split; when the friction significantly differs between the left and the right wheelpath. The road may then not be perceived as hazardous when accelerating, cruising or even braking softly, but in a case of hard braking, the difference in friction will cause the vehicle to start to rotate towards the side offering higher grip. Split friction may cause jack-knifing of articulated trucks, while trucks with towed trailers may experience trailer swing phenomena. Split friction may be caused by an improper road spot repair that results in high variance of texture (roads) and colour (thin ice on newly paved black spots thaws faster than ice on old greyish asphalt) across the road section.

Solomon curve

The Solomon curve is a graphical representation of the collision rate of automobiles as a function of their speed compared to the average vehicle speed on the same road. The curve was based on research conducted by David Solomon in the late 1950s and published in 1964. Subsequent research suggests significant biases in the Solomon study, which may cast doubt on its findings.

Stop sign

A stop sign is a traffic sign designed to notify drivers that they must come to a complete stop and make sure no other vehicles are coming and no pedestrians are crossing before proceeding.

Traffic calming

Traffic calming uses physical design and other measures to improve safety for motorists, pedestrians and cyclists. It aims to encourage safer, more responsible driving and potentially reduce traffic flow. Urban planners and traffic engineers have many strategies for traffic calming, including narrowed roads and speed humps. Such measures are common in Australia and Europe (especially Northern Europe), but less so in North America. Traffic calming is a calque (literal translation) of the German word Verkehrsberuhigung – the term's first published use in English was in 1985 by Carmen Hass-Klau.

Traffic collision

A traffic collision, also called a motor vehicle collision (MVC) among other terms, occurs when a vehicle collides with another vehicle, pedestrian, animal, road debris, or other stationary obstruction, such as a tree, pole or building. Traffic collisions often result in injury, death, and property damage.

A number of factors contribute to the risk of collisions, including vehicle design, speed of operation, road design, road environment, and driver skill, impairment due to alcohol or drugs, and behavior, notably distracted driving, speeding and street racing. Worldwide, motor vehicle collisions lead to death and disability as well as financial costs to both society and the individuals involved.

In 2013, 54 million people worldwide sustained injuries from traffic collisions. This resulted in 1.4 million deaths in 2013, up from 1.1 million deaths in 1990. About 68,000 of these occurred in children less than five years old. Almost all high-income countries have decreasing death rates, while the majority of low-income countries have increasing death rates due to traffic collisions. Middle-income countries have the highest rate with 20 deaths per 100,000 inhabitants, accounting for 80% of all road fatalities with 52% of all vehicles. While the death rate in Africa is the highest (24.1 per 100,000 inhabitants), the lowest rate is to be found in Europe (10.3 per 100,000 inhabitants).

Traffic collision reconstruction

Vehicular collision reconstruction is the scientific process of investigating, analyzing, and drawing conclusions about the causes and events during a vehicle collision. Reconstructionists are employed to conduct in-depth collision analysis and reconstruction to identify the collision causation and contributing factors in different types of collisions, including the role of the driver(s), vehicle(s), roadway and the environment. The laws of physics and engineering principles such as the conservation of linear momentum, work-energy methods, and kinematics are the basis for these analyses and may make use of software to calculate useful quantities. The collision reconstruction provides rigorous analysis that an expert witness can present at trial. Collision reconstructions are done in cases involving fatalities, and often when personal injury is involved. Results from collision reconstructions are also useful in developing recommendations for making roads and highways safer, as well as improving safety aspects of motor vehicle designs. These reconstructions are often conducted by forensic engineers, specialized units in law enforcement agencies, or private consultants.

Traffic stop

A traffic stop, commonly called being pulled over, is a temporary detention of a driver of a vehicle by police to investigate a possible crime or minor violation of law.

Traffic violations reciprocity

Under traffic violations reciprocity agreements, non-resident drivers are treated like residents when they are stopped for a traffic offense that occurs in another jurisdiction. They also ensure that punishments such as penalty points on one's license and the ensuing increase in insurance premiums follow the driver home. The general principle of such interstate, interprovincial, and/or international compacts is to guarantee the rule "one license, one record."

Rules of the road
Road user guides
Speed limit
Moving violations
Driver licensing
Traffic violations reciprocity
Automotive safety
Road safety
Self-driving cars and enabling technologies
Overview and context
SAE Levels
Enabling technologies
Organizations, Projects & People

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