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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]

Contents

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

Origins

As with the genesis of most legal doctrine governing problems which precede a legislative solution, the ACDA principle generally originates to decisional precedent by high courts which 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]

Present

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 road's 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]

Intersections
Visual Limits of Drivers Entering Intersection from a Stop.
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Head-on Car Speed vs. Detection Distance of Looming Motion [17]
For an onlooker without assistance of lateral movement. [118] [119]
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Lateral Car Speed vs. Detection Distance of Lateral Motion [120]
For an onlooker without assistance of looming movement. [118] [119]

As a vehicle creeps into an intersection, the lateral perspective diminishes until head-on looming motion is the more insightful of the two. Both lateral and looming motion may also combine somewhat to enhance detection according to Gestalt Theory, permitting they are both observable.

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 decelerate [133] [125] [54] [126] and apply the ACDA principle specifically to the intersection. [1] [13] [35] [112] [15] See Table of detection thresholds.

Technical ACDA Theory of Intersections

When approaching an un-signalized intersection controlled by a stop sign, the assured clear distance ahead is:

${\displaystyle ACDA_{si}=V\left({\sqrt {\frac {2d_{i}}{a_{i}}}}+t_{pc}\right)}$

Normal acceleration "ai" for a passenger vehicle from a stop up to 20 mph is about 0.15g, with more than 0.3g being difficult to exceed. [124] The distance "di" is the sum of the measured limit line setback distance—which is typically regulated by a Manual on Uniform Traffic Control Devices, at often between 4 and 30 feet in the United States [134] [135] [136] —and the crosswalk, parking lane, and road shoulder width. A vehicle accelerating from a stop travels this distance in time ti=2diai while through traffic travels a distance equal to their speed multiplied by that time. The time tpc, for the stopped motorist, is the sum of perception time and the time required to actuate an automatic transmission or shift to first gear which is usually between 12 to one second. [137]

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:

${\displaystyle ACDA_{si}={\frac {Vd_{hsd}}{V_{i}}}}$

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.

Measurement

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.

Discretion

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:

${\displaystyle \color {Sepia}{t\approx {\frac {v}{20}}+1\quad {\text{(seconds of distance to stop rule)}}}}$

If this distance is greater than the ACDA, they need to decelerate. 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:

${\displaystyle V_{BSL}={\begin{cases}{\sqrt {(\mu +e)^{2}g^{2}t_{prt}^{2}+2(\mu +e)gd_{ACDA_{s}}}}-(\mu +e)gt_{prt},&{\text{if }}V_{ACDA_{s}}\leq V_{ACDA_{si1}}{\text{ or }}V_{ACDA_{si2}}{\text{ or }}V_{ACDA_{d}}{\text{ or }}V_{cs}{\text{ or }}V_{cl}\\\\2g(\mu +e)({\frac {d_{hsd}}{v_{i}}}-t_{prt}),&{\text{if }}V_{ACDA_{si1}}

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.

${\displaystyle e=\sin(\theta )\approx \theta \approx \tan(\theta )={\frac {\%{\text{grade}}}{100}}}$

[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 ${\displaystyle V_{ACDA_{s}}}$, the friction coefficient is symbolized by ${\displaystyle \mu }$—and itself a function of the tire type and road conditions, the distance ${\displaystyle d_{ACDA_{s}}}$ is the static ACDA, the constant ${\displaystyle g}$ is the acceleration of gravity, and interval ${\displaystyle t_{prt}}$ is the perception-reaction time—usually between 1.0 and 2.5 seconds. [145] [146]

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 km/h). 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.

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.

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]

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

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 warn them it knocked down a tree in a forest with many trees which all eventually fell. In this specific regard, jurisdictions which grant drivers the liberty to be fools from their own folly, are also condoning the collateral damage and life loss which is expected to occur. Moreover, modern life-entrusting consumers of 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]

Derivations

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

Derivation of ACDA 1

Starting with Newton's Second Law of Motion and the Laws of Friction:

${\displaystyle F_{\text{total}}=F_{\text{friction}}+F_{\text{gravity}}\sin \theta }$
${\displaystyle F_{\text{total}}=\mu F_{\text{normal}}+mg\sin \theta }$
${\displaystyle F_{\text{total}}=\mu mg\cos {\theta }+mg\sin \theta }$

Equating the net force to mass times acceleration:

${\displaystyle F_{\text{total}}=ma}$
${\displaystyle \mu mg\cos \theta +mg\sin \theta =ma}$
${\displaystyle a=g(\mu \cos \theta +\sin \theta )}$

Invoking the equations of motion and substituting acceleration:

${\displaystyle d={\frac {v^{2}}{2a}}}$
${\displaystyle d={\frac {v^{2}}{2g(\mu \cos \theta +\sin \theta )}}}$
${\displaystyle \sin \theta \approx \theta }$
${\displaystyle \cos \theta \approx 1-{\frac {\theta ^{2}}{2}}}$

Substituting the small angle approximations, and exploiting that the product of a small angle squared, in radians, with the friction coefficient, θ2μ, is insignificant (for a steep 20% slope and a good friction coef. of 0.8, this equals (.2)2x0.8≈0.03):

${\displaystyle d\approx {\frac {v^{2}}{2g[\mu (1-{\frac {\theta ^{2}}{2}})+\theta ]}}\approx {\frac {v^{2}}{2g(\mu +\theta )}}}$

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

${\displaystyle d_{\text{total}}=d_{\text{braking}}+d_{\text{perception-reaction}}}$
${\displaystyle d_{\text{total}}\approx {\frac {v^{2}}{2g(\mu +\theta )}}+vt_{pr}}$

Isolating zero as preparation to solve for velocity:

${\displaystyle {\frac {1}{2g(\mu +\theta )}}v^{2}+vt_{prt}-d_{\text{total}}\approx 0}$

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

${\displaystyle v\approx {\sqrt {(\mu +\theta )^{2}g^{2}t_{prt}^{2}+2(\mu +\theta )gd_{\text{total}}}}-(\mu +\theta )gt_{prt}}$

Use small-angle approximation to obtain a more field-able version of the above solution in terms of percent grade/100 "e" instead of an angle θ in radians:

${\displaystyle \theta \approx \tan(\theta )={\frac {\%{\text{grade}}}{100}}}$

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

${\displaystyle V_{BSL1}\approx {\sqrt {(\mu +e)^{2}g^{2}t_{prt}^{2}+2(\mu +e)gd_{ACDA}}}-(\mu +e)gt_{prt}}$

The Basic Speed Law constrains the assured clear distance ahead to the total stopping distance, and the small angle value of road grades approximates the superelevation "e."

Many roadways are level, in which case the small angle approximations or superelevation may be dropped altogether:

${\displaystyle V_{BSL1}={\sqrt {\mu ^{2}g^{2}t_{prt}^{2}+2\mu gd_{ACDA}}}-\mu gt_{prt}}$

This model ignores the effects of air drag, rolling resistance, lift, and relativity as a vehicle's great momentum and weight dominate these factors; they increase the complexity of the formulas while insubstantially changing the outcomes in practically all driving situations except ultra-low-mass bicycles stopping from inherently dangerously high speeds; usability to the layman and conformance with current standard engineering assumptions [106] [107] is the objective and a vehicle's lift factor is often inaccessible. Learn a level ground model with most of those effects here or read about the automobile drag coefficient.

Case 2: Safe speed as a function of horizontal line-of-sight

Derivation of ACDA 2

The time required for an obstruction with speed vi to transect the horizontal sight distance di:

${\displaystyle t={\frac {d_{i}}{v_{i}}}}$

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

${\displaystyle t={\frac {d}{v}}}$

Equating the two times:

${\displaystyle {\frac {d}{v}}={\frac {d_{i}}{v_{i}}}}$

Solving for this distance:

${\displaystyle d={\frac {vd_{i}}{v_{i}}}}$

Equating this to the total stopping distance, which is the sum of braking and perception-reaction distances:

${\displaystyle {\frac {vd_{i}}{v_{i}}}={\frac {v^{2}}{2g(\mu +e)}}+vt_{prt}}$

Isolating zero, and factoring out a v:

${\displaystyle v\left[{\frac {v}{2g(\mu +e)}}+\left(t_{prt}-{\frac {d_{i}}{v_{i}}}\right)\right]=0}$

Solving for the non-trivial case (or may distribute v in equation above and apply quadratic formula for same result):

${\displaystyle {\frac {v}{2g(\mu +e)}}+(t_{prt}-{\frac {d_{i}}{v_{i}}})=0}$

The solution to the above equation, which provides the maximum safe speed as a function of horizontal sight distance, intercept velocity, and road-tire friction coefficient:

${\displaystyle v=2g(\mu +e)({\frac {d_{i}}{v_{i}}}-t_{prt})}$

Case 3: Safe speed as a function of intersectional setback

Derivation of ACDA 3

The time required for a vehicle to enter a controlled intersection from a stop is the sum of the perception time (tp), the time required to actuate an automatic transmission or shift to first gear (tc), and the time to accelerate and enter or traverse the road (ta). The sum of the first two quantities is tpc.

${\displaystyle t=t_{p}+t_{c}+t_{a}=t_{pc}+t_{a}}$

The time required for a vehicle entering with acceleration ai to transect the sum of the setback and shoulder distances di under uniform acceleration ai from a stop via the equations of motion:

${\displaystyle t_{a}={\sqrt {\frac {2d_{i}}{a_{i}}}}}$

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

${\displaystyle t={\frac {d}{v}}}$

Equating the two times:

${\displaystyle {\frac {d}{v}}={\sqrt {\frac {2d_{i}}{a_{i}}}}+t_{pc}}$

Solving for this distance:

${\displaystyle d=v\left({\sqrt {\frac {2d_{i}}{a_{i}}}}+t_{pc}\right)}$

Equating this to the total stopping distance, which is the sum of braking and perception-reaction distances:

${\displaystyle v\left({\sqrt {\frac {2d_{i}}{a_{i}}}}+t_{pc}\right)={\frac {v^{2}}{2g(\mu +e)}}+vt_{prt}}$

Isolating zero, and factoring out a v:

${\displaystyle v[{\frac {v}{2g(\mu +e)}}+\left(t_{prt}-{\sqrt {\frac {2d_{i}}{a_{i}}}}-t_{pc}\right)]=0}$

Solving for the non-trivial case (or may distribute v in equation above and apply quadratic formula for same result):

${\displaystyle {\frac {v}{2g(\mu +e)}}+\left(t_{prt}-{\sqrt {\frac {2d_{i}}{a_{i}}}}-t_{pc}\right)=0}$

The solution to the above equation, which provides the maximum safe speed as a function of horizontal setback, intercept acceleration, and road-tire friction coefficient:

${\displaystyle v=2g(\mu +e)\left({\sqrt {\frac {2d_{i}}{a_{i}}}}+t_{pc}-t_{prt}\right)}$

Case 4: Safe speed as a function of following distance

Derivation of ACDA 4

From the equations of motion:

${\displaystyle t_{g}={\frac {d}{v}}}$

Isolating for speed:

${\displaystyle v={\frac {d}{t_{g}}}}$

Case 5: Safe speed as a function of critical speed

Derivation of ACDA 5

Starting with Newton's Laws of Motion, the Laws of Friction, and Centripetal force:

${\displaystyle F_{\text{centripetal}}\cos {\theta }=F_{\text{friction}}+F_{\text{gravity}}\sin \theta }$

Substituting formulas for Centripetal force, frictional force, and gravitational force:

${\displaystyle m{\frac {v^{2}}{r}}\cos \theta =\mu F_{\text{normal}}+mg\sin \theta }$

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

${\displaystyle m{\frac {v^{2}}{r}}\cos \theta =\mu (mg\cos {\theta }+m{\frac {v^{2}}{r}}\sin \theta )+mg\sin \theta }$

Isolate ${\displaystyle v}$ terms:

${\displaystyle {\frac {v^{2}}{r}}\cos \theta -\mu {\frac {v^{2}}{r}}\sin \theta =g(\mu \cos \theta +\sin \theta )}$

Then solve for ${\displaystyle v}$:

${\displaystyle v^{2}(\cos \theta -\mu \sin \theta )=gr(\mu \cos \theta +\sin \theta )}$

To obtain:

${\displaystyle v={\sqrt {\frac {gr(\mu \cos \theta +\sin \theta )}{\cos \theta -\mu \sin \theta }}}}$

This is the full solution, however most corners are banked at less than 15 degrees (≈28% grade), so in such conditions, a fieldable small angle approximation may be used.

Substituting small-angle approximations sin θ  θ, cos  1  θ2/2:

${\displaystyle v\approx {\sqrt {\frac {gr[\mu (1-{\frac {\theta ^{2}}{2}})+\theta ]}{1-{\frac {\theta ^{2}}{2}}-\mu \theta }}}}$

Exploit that a small angle squared, in radians, is insignificant by substituting θ2≈0 which obtains the formula used in case 5 (also tan θ≈e):

${\displaystyle v\approx {\sqrt {\frac {gr(\mu +\theta )}{1-\mu \theta }}}\approx {\sqrt {\frac {gr(\mu +e)}{1-\mu e}}}}$

Seconds of distance to stop rule

Derivation of Seconds of distance to stop rule

The seconds-of-distance-to-stop rule is derived as follows.

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

${\displaystyle d_{\text{total}}=d_{\text{braking}}+d_{\text{perception-reaction}}}$

Invoking the equations of motion,

${\displaystyle d_{\text{braking}}={\frac {v^{2}}{2a}}}$
${\displaystyle d_{\text{total}}={\frac {v^{2}}{2a}}+vt_{\text{prt}}}$

where

${\displaystyle a=\mu g}$.

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

${\displaystyle t={\frac {d_{\text{total}}}{v}}}$.

Substituting the former into the latter,

${\displaystyle t={\frac {v}{2\mu g}}+t_{\text{prt}}}$.

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

${\displaystyle t=C\cdot v+t_{\text{prt}}}$

by noting that

${\displaystyle C={\frac {f}{2\mu g}}}$.

Substituting (US Customary units)

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

we have

${\displaystyle C={\tfrac {1}{30}}}$ (dry), ${\displaystyle {\tfrac {1}{20}}}$ (wet), and ${\displaystyle {\tfrac {1}{10}}}$ (snow).

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

${\displaystyle t={\frac {v}{30}}+1.5}$ (dry pavement)
${\displaystyle t={\frac {v}{20}}+1.5}$ (wet pavement)
${\displaystyle t={\frac {v}{10}}+1.5}$ (snow, hard-packed).

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

${\displaystyle \color {Sepia}{t\approx {\frac {v}{20}}+1\quad {\text{(general rule of thumb)}}}}$(instead add 2+ in wet or complex conditions, and also instead divide by 10 in snow/ice)

For example, a speed of 60 miles per hour (97 km/h) corresponds to stopping distance of 4 seconds' travel at 60 mph. Drivers that require additional perception-reaction time, such as novices, elderly, or those in complex or adverse environments, can benefit by adding additional seconds. [183] [184]

The time to traverse your stopping distance at travel speed should not be confused with the braking time to come to a full stop, which is a number nearly twice this value ( t=v/μ g+tptr ). As one is continually slowing down while braking, it will naturally take longer to get to the stopping limit.

A more correct perception-reaction time of one-and-a-half seconds is commonly used by the mathematically inclined. [107] [146] Doing so to obtain your "seconds-of-distance-to-stop" for dry pavement and then converting time to actual distance by multiplying it by the travel velocity and 22/15 to convert MPH to fps will yield results in close agreement with this table.

Whereas most driving is done below 80 miles per hour (130 km/h), maintaining a blanket 5 or 6 seconds of travel time to the edge of visibility (t=80/20+1), will keep drivers in compliance with the ACDA rule in most simple highway driving conditions – day or night – with growing error towards safety at lower speeds.

On final note, slope has an effect on stopping distance. An additional second or so will need to be added when stopping while traveling down a steep incline, and conversely driving uphill will improve breaking. [106] This is accounting that a level road was assumed in the rule of thumb. See more general derivation here

Tables of reference constants and safe speeds

Reference constants

Table of perception-reaction times

Table of perception-reaction times
Perception-reaction times [seconds] [145] [185]
Anticipated objectUnexpected objectUnexpected signal
0.721.281.27

Average value of tire friction coefficient [186]
Road surfacePeak value (μs)Sliding value (μd)
Asphalt and concrete (dry)0.80 − 0.900.75
Asphalt (wet)0.50 − 0.700.45 − 0.60
Concrete (wet)0.800.70
Gravel0.600.55
Snow (hard-packed)0.200.15
Ice0.100.07

Table of acceleration values

Table of acceleration values
Acceleration values [124]
CarTruckBicycle
0.15g0.085–0.138g [187]

Table of intercept values

Table of intercept values
Approach speeds of hazards which may foreseeably intercept the roadway
pedestrian(walk/run)bicyclecatdogdeerelk
3.1–5.6 mph/27.78 mph [188] 14.7f/s [189] 29.8 mph63.5 km/h48.2 km/h72.4 km/h

See more animal intercept speeds. See article on speed.

Table of tire speed ratings

Table of tire speed ratings
Tire speed rating [190]
Codemphkm/hCodemphkm/h
A135L75120
A2610M81130
A3915N87140
A41220P94150
A51625Q100160
A61930R106170
A72235S112180
A82540T118190
B3150U124200
C3760H130210
D4065V149240
E4370Zover 149over 240
F5080W168270
G5690(W)over 168over 270
J62100Y186300
K68110(Y)over 186over 300

See article on tire codes.

Safe speeds

Table of ACDA: forward line-of-sight

Table of ACDA: forward line-of-sight
Average safe speed as a function of assured clear distance ahead [107]
ACDA [meters]ACDA [feet]Safe speed [km/h]Safe speed [mph]
13.32.31.4
2.58.25.63.5
413.18.65.3
5.518.011.47.1
723.014.18.8
8.527.916.710.4
1032.819.111.9
15492716
30984528
451486037
601977345
752468452
902959559
10534410565
12039411471
13544312276
15049213081
16554113886
18059114691
19564015395
21068916099
225738166103
240787173107
255837179111
270886185115
285935191119
300984197122

The speed values in this table are produced from the formula using an "average" coefficient of friction (μ) of 0.7, and a perception-reaction time of 1.5 seconds. Speed values specific to a given circumstance can be obtained with the same formula using the appropriate reference constants specific to the circumstance.

${\displaystyle V_{BSL}={\sqrt {(\mu +e)^{2}g^{2}t_{prt}^{2}+2(\mu +e)gd_{ACDA_{s}}}}-(\mu +e)gt_{prt}}$

Table of ACDA: horizontal line-of-sight

Table of ACDA: horizontal line-of-sight
Safe speed as a function of horizontal clearance for 9 km/h (5.6 mph) intercept object (i.e. child)
HSD [meters]HSD [feet]Safe speed [km/h]Safe speed [mph]
3.01000
4.013.14.93.1
4.514.814.89.2
5.016.424.715.4
5.518.034.621.5
6204428
7236440
8268452
93010465
103312477
113614389
1239163101

This table demonstrates why alleyways, parking lots, parks, and residential areas frequently set 5–15 mph speed limits when the side clearance from the road is less than 15 feet. An urban or residential street which permits a maximum speed limit of 25 mph under its very best conditions (roadsides cleared of visual obstructions past a 20-foot maintained right of way), may in practice be unsafe to drive at more than 10 mph within sections with utilized curbside parking. This table also suggests that the safe speed could be greater than a statutory 25 mph posted speed, where roadside clearance is sufficient such that no "foreseeable" object could emerge from the proximate edge of roadside visibility, transect the cleared area, and intercept the lane before the driver could come to a halt. However, wary road design engineers may have differing views of foreseeable intercept speeds than that reflected by the 85th percentile speed chosen by the public. This can have unfortunate consequences where a mass commuting public is unfamiliar with or does not appreciate specific local hazards. Narrow lane widths are purposely used for traffic calming, because careful drivers universally choose their speed depending on the roadway width. [191] Standard horizontal clearances are commonly set by AASHTO guidelines or a jurisdiction's department of transportation. [106] [192]

Safe speed as a function of horizontal clearance for 16 km/h (10 mph) intercept object (i.e. domestic animals)
HSD [meters]HSD [feet]Safe speed [km/h]Safe speed [mph]
72342
826159
9302616
10333723
11364830
12395937
13437044
14468251
15499358
165210465
175611571
185912678
196213785
206614892
216915999
2272171106
2375182113
2479193120
2582204127
Safe speed as a function of horizontal clearance for 48.2 km/h (30 mph) intercept object (i.e. deer)
HSD [meters]HSD [feet]Safe speed [km/h]Safe speed [mph]
206600
216932
227274
2375117
2479149
25821811
26852214
27892616
28922918
29953320
30983723
311024025
321054427
331084830
341125132
351155534
361185937
371216239
381256641
391287043
401317446
411357748
421388150
431418553
441448855
451489257
461519659
471549962
4815710364
4916110766
5016411069

The speed values in these tables are produced from the formula using an "average" coefficient of friction (μ) of 0.7, and a perception-reaction time of 1.5 seconds. Speed values specific to a given circumstance can be obtained with the same formula using the appropriate reference constants specific to the circumstance.

${\displaystyle V_{BSL}=2g(\mu +e)({\frac {d_{hsd}}{v_{i}}}-t_{prt})}$

Table of ACDA: intersectional setback

Table of ACDA: intersectional setback
Approach speed as a function of setback distance (acceleration=0.15g) [193]
Setback [meters]Setback [feet]Approach speed [m/s]
000
0.51.611.3
1316
1.54.919.6
2723
31028
41332
51636
62039
82645
103351
123955
144660
165264
185968
206672
227275
247978
268582
289285
309888

Speed values specific to a given circumstance can be obtained with the same formula using the appropriate reference constants specific to the circumstance.

${\displaystyle V_{BSL}=2g(\mu +e)\left({\sqrt {\frac {2d_{sl}}{a_{i}}}}+t_{pc}-t_{prt}\right)}$

Table of following distances

Table of following distances (2 second rule)
Following distance (2 second rule)
Speed [km/h]Speed [mph]Following distance [meters]Following distance [feet]
0000
5339
106618
159827
20121136
25161446
30191755
35221964
40252273
45282582
50312891
553431100
603733109
654036118
704339128
754742137
805044146
855347155
905650164
955953173
1006256182
1056558191
1106861200
1157164210
1207567219
1257869228
1308172237
1358475246
1408778255
1459081264
1509383273

Table of critical speeds

Table of critical speeds
Average physical critical speeds on level surface (e=0, μ=0.7)
516.421.113.1
10333019
20664226
30985232
401316037
501646741
601977345
702307949
802628452
902958956
1003289459
1103619961
12039410364
13042710867
14045911269
15049211672
16052511974
17055812376
18059112779
19062313081
20065613383

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

Average psychological critical speeds on level surface (e7 = 0, μ = 0.3) [148]
516149
10332012
15492415
20662817
25823119
30983421
351153723
401313924
451484126
501644427
551804628
601974830
652135031
702305232
752465333
802625534
852795735
902955936
953126037
1003286238
1053446339
1103616540
1153776641
1203946842
1254106943
1304277044
1404597345
1454767446
1504927647
1555097748
1605257849
1705588150
1755748251
1805918351
1856078452
1906238553
2006568754
2056738855
2106898956
2207229257
2307559458
2407879659
2458049760
2508209861
26085310062
28091910364
30098410766
320105011069
340111511471
360118111773
380124712075
400131212477
420137812779
440144413080
460150913282
480157513584
500164013886

Most motorists will not tolerate a lateral acceleration exceeding 0.3g (μ=0.3) above which many will panic. [148]

Speed values specific to a given circumstance can be obtained with the same formula using the appropriate reference constants specific to the circumstance.

${\displaystyle V_{BSL}={\sqrt {\frac {(\mu +e)gr}{1-\mu e}}}}$

Table of detection thresholds

Table of detection thresholds: SAVT
Table of detection thresholds: looming motion of a car θt=0.0397-0.0117, S=6ft [16] [17] [194] [195]
Speed [KM/H]Speed [MPH]Detection distance [m]Detection distance [ft]Time to collision [s]
533–615–8
1047–873–6
1558–1063–5
2067–1232–4
2574–1372–4
3081–1502–3
3588–1622–3
4094–1732–3
45100–1842–3
50105–1941–3
55110–2031–3
60115–2121–2
65120–2211–2
70125–2291–2
75129–2371–2
80133–2451–2
Table of detection thresholds: looming motion of tractor-trailer θt=0.0397-0.0117, S=8ft [16] [17] [194]
Speed [KM/H]Speed [MPH]Detection distance [m]Detection distance [ft]Time to collision [s]
538–715–10
1054–1004–7
1566–1233–6
2077–1423–5
2586–1582–4
3094–1732–4
35102–1872–4
40109–2002–3
45115–2122–3
50121–2242–3
55127–2352–3
60133–2452–3
65139–2551–3
70144–2651–3
75149–2741–2
80154–2831–2

For a person with SAVT limit of ${\displaystyle {\dot {\theta }}_{t}}$, the looming motion of a directly approaching object of size S, moving at velocity v, is not detectable until its distance D is [129]

${\displaystyle D\lessapprox {\sqrt {{\frac {S\cdot v}{\dot {\theta _{t}}}}-{\frac {S^{2}}{4}}}}}$

Notes

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, ${\displaystyle {\dot {\theta }}_{t}}$. Given a vehicle of size ${\displaystyle S}$ and distance ${\displaystyle x}$, the visual angle is: ${\displaystyle \theta =2\arctan {\left({\tfrac {S}{2x}}\right)}}$. Its derivative with respect to distance is ${\displaystyle {\tfrac {d\theta }{dx}}={\tfrac {-4S}{S^{2}+4x^{2}}}}$. An approaching vehicle of constant velocity ${\displaystyle v}$ will decrease the distance at rate ${\displaystyle {\tfrac {dx}{dt}}=-v}$. 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: ${\displaystyle {\tfrac {d\theta }{dt}}={\tfrac {\mathrm {d} \theta }{\mathrm {d} x}}\cdot {\tfrac {\mathrm {d} x}{\mathrm {d} t}}}$. It follows that ${\displaystyle {\frac {4S\cdot v}{S^{2}+4x^{2}}}\gtrsim {\dot {\theta _{t}}}}$. Hence, an approaching vehicle's looming motion is not perceivable until ${\displaystyle x\lesssim {\sqrt {{\frac {S\cdot v}{\dot {\theta _{t}}}}-{\frac {S^{2}}{4}}}}}$, 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.
${\displaystyle V_{ACDA(s)}={\sqrt {\mu ^{2}g^{2}t_{prt}^{2}+2\mu gd_{ACDA_{s}}}}-\mu gt_{prt}}$
For example, using the ${\displaystyle \mu =0.7}$ and ${\displaystyle t_{prt}=1.5}$ 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:
${\displaystyle V_{ACDA}\approx {\sqrt {1372.3+177.8d_{ACDA}}}-37.0}$
US customary – Speed in MPH from distance in feet:
${\displaystyle V_{ACDA}\approx {\sqrt {529.8+20.9d_{ACDA}}}-23.0}$
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.

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References

2. 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. 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. 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. Newton v. Stebbins, 51 U.S. 586, 51United States Reports586 ( 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. 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. Connally v. General Construction Co. , 269United States Reports385 , 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. State of Montana, v. Rudy Stanko, 1998MT321 , 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. 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. Le Vine, Scott; Liu, Xiaobo; Zheng, Fangfang; Polak, John (January 1, 2016). "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. Reaugh v. Cudahy Packing Co., 189 Cal. 335, 189Official California Reports335 ( 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. Morris v. Jenrette Transport Co., 235N.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."...it was his duty to anticipate presence of others, [...] and hazards of the road, such as disabled vehicle, and, in the exercise of due care, to keep his automobile under such control as to be able to stop within the range of his lights").
15. Allin v. Snavely, 100 Cal. App. 2d 411, 100Official California Appellate Reports, 2nd Series411 ( 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. 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. PMID   8870768. 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. 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. S2CID   109898296. 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. The Batavier, 40English Reports in Law and Equity19–27 , 25(Great Britain. Courts.; Great Britain. Parliament. House of Lords.; Great Britain. Privy Council. Judicial CommitteeJuly 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. The Europa, 2English Reports in Law and Equity557–564 , 564(Great Britain. Courts.; Great Britain. Parliament. House of Lords.; Great Britain. Privy Council. Judicial CommitteeJune 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. The Colorado, 91 U.S. 692, 91United States Reports692 ( 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. Lauson v. Town of Fond du Lac, 141 Wis. 57, 123 N. W. 629, 25 L. R. A. (N. S.) 40.,141Wis.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. Garner v. Maxwell, 360 S.W.2d 64, 360S.W.2d64 ( 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. The Nacoochee v. Moseley, 137 U.S. 330, 137United States Reports330 ( 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. Curtis v. Hubbel, 42 Ohio App. 520, 182 N. E. 589, 42Ohio 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. Lindquist v. Thierman, 216 Iowa 170, 216Iowa170 ( Iowa Supreme Court 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, 66United States Reports459 , 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, 335United States Reports1 , 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. 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. Cook v. Miller, 175 Cal. 497, 175Official California Reports497 ( 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. "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, 96Indiana Appellate Reports71 ( 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, 234La.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, 146So.2d451 (Court of Appeal of Louisiana. Fourth CircuitOctober 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),219Mich.110(1922).
45. Gleason v. Lowe, 232 Mich. 300, 232Mich.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. Ruth v. Vroom, 245 Mich. 88, 222 N. W. 155, 62 A. L. R. 1528, 245Mich.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. O'Farrell v. Inzeo, 74 A.D.2d 806 (1st Dept. 1980), 74A.D.2d806 ( 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., 49Ohio St.2d5 , 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, 104Vt.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. 415,217Wis.465( Wisconsin Supreme Court 1935).
52. Satterlee v. Orange Glenn School Dist., 29 Cal.2d 581, 29Official California Reports, 2nd Series581 ( 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. Wilding v. Norton, 156 Cal.App.2d 374, 156Official California Appellate Reports, 2nd Series374 ( 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. Whitelaw v. McGilliard,179 Cal. 349, 179Official California Reports349 ( 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, 175Official California Appellate Reports, 2nd Series140 ( 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 March 25, 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 July 3, 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 September 28, 2013. Retrieved August 27, 2013. 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, 366Mich.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. "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.
72. 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
73. "North Carolina Driver's Handbook" (PDF). N.C. Division of Motor Vehicles. pp. 51, 66. Archived from the original (PDF) on March 4, 2016. Retrieved February 25, 2016. 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
74. Driver's Manual (PDF). Oklahoma Department of Public Safety. pp. 8–2.
75. Driver's Manual (PDF). Iowa Department of Transportation. p. 39.
78. "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.
79. Baltimore & Ohio R. Co. v. Goodman, 275 U.S. 66, 275United States Reports66 ( 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.").
80. 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.
81. "Federal Motor Vehicle Safety Standards; Event Data Recorders". Federal Register. December 12, 2012.
82. "Event Data Recorder Supported Vehicles" (PDF). Rimkus Consulting Group, Inc. July 2015. Archived from the original (PDF) on March 11, 2016. Retrieved February 26, 2016.
83. "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."
84. "Urban Street Design Guide". National Association of City Transportation Officials. April 8, 2015. 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.
85. "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.
86. Eloisa Raynault; Ed Christopher (May 2013). "How Does Transportation Affect Public Health? (FHWA-HRT-13-004)". Public Roads. 76 (6).
87. "CDC Transportation Recommendations". Atlanta, GA: Centers for Disease Control and Prevention. February 7, 2018. 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.
88. "Smart Growth and Transportation". Washington, DC: United States Environmental Protection Agency. April 26, 2013. 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.
89. "Transportation". Smart Growth America. December 17, 2019. 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.
90. "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.
91. "Transportation Choices for Sustainable Communities". January 17, 2014.
92. "What is universal access?". humantransport.org. July 29, 2021. 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.
93. "Assured Clear Distance Ahead and Vision Zero". BikeWalk NC. October 2015.
94. William Kenworthy (January 1, 2000). Killer Roads: From Crash to Verdict (2nd ed.). Lexis Law Pub. ISBN   978-0327100164.
95. Van Praag v. Gale,107Cal438( 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.").
96. Doyle v. Eschen, 5Cal.App55 ( 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.").
97. Malinson v. Black, 83Cal.App.2d375 , 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.").
98. ""Martin-Quinn" measures of judicial ideology". University of California. Archived from the original on March 7, 2016.
99. Andrew Cabasso (September 3, 2015). "Vehicles Lawyers Should Not Drive". Lawyerist.com. 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.
100. "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.
101. United States v. National City Lines, Inc., et al, 186F.2d562 ( 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 therewith...as National and Pacific acquired local transportation systems in the other sections of the country, those markets would be allocated to and preempted by a company selling petroleum products in such sections...").
102. 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 1920s the major part of the traffic regulation was by municipalities; it had mainly been enacted ten to fifteen years before and hence left out of account the vast increase in number, speed, and use of automobiles. Each town and city had a different set of rules, confusing the motorist on tour. This dangerous chaos has been largely obviated by the substantial enactment in most states of the Uniform Act...
103. 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
104. A Policy on Geometric Design of Highways and Streets (6th ed.). American Association of State Highway and Transportation Officials. 2011. ISBN   978-1560515081.
105. "Tables of speed and stopping distances". The State of Virginia.
106. Cannon v. Kemper, 23 Cal. App. 2d 239, 23Official California Appellate Reports, 2nd Series239 ( 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
107. Hatzakorzian v. Rucker-Fuller Desk Co., 197 Cal. 82, 197Official California Reports82 ( 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.."").
108. Bove v. Beckman, 236 Cal. App. 2d 555, 236Official California Appellate Reports, 2nd Series555 ( 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
109. Falasco v. Hulen, 6 Cal. App. 2d 224, 6Official California Appellate Reports, 2nd Series224 ( 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
110. Riggs v. Gasser Motors, 22 Cal. App. 2d 636, 22Official California Appellate Reports, 2nd Series636 ( 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 law...is always governing.""). See Official Reports Opinions Online
111. 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.
113. Leeper v. Nelson, 139 Cal. App. 2d 65, 139Official California Appellate Reports, 2nd Series65 ( 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
115. 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.
116. Malinson v. Black, 83 Cal. App. 2d 377, 83Official California Appellate Reports, Second Series377 ( 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. ").
117. Nevis v. Pacific Gas & Electric Co., 43 Cal.2d 626, 43Official California Reports, Second Series626 ( 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 ").
118. 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:. PMID   19271900. Displacement thresholds for peripheral motion were affected by acuity limits for speeds below 0.5 degrees/s. [0.0087 radians/s]
119. "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.
120. "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.
121. "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.
122. J. Stannard Baker (1963). Traffic Accident Investigator's Manual for Police (2 ed.). The Traffic Institute, Northwestern University. pp. 43–48. LCCN   62-20895.
123. Grasso v. Cunial, 106 Cal. App. 2d 294, 106California Official Reports, 2nd Series294 ( 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 ").
124. Page v. Mazzei, 213 Cal. 644, 213Official California Reports644 ( 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 ").
125. Fitts v. Marquis, 127 Me. 75, 127Maine Reporter75 ( 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.").
126. 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.
127. Hershel Weinberger (February 19, 1971). "Conjecture on the Visual Estimation of Relative Radial Motion". Nature . 229 (5286): 562. Bibcode:1971Natur.229..562W. doi:. PMID   4925353. S2CID   4290244.
128. 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): 30.1–14. doi:. PMID   19271900. Displacement thresholds for peripheral motion were affected by acuity limits for speeds below 0.5 degrees/s.
129. Paul R. Schrater; David C. Knill; Eero P. Simoncelli (April 12, 2001). "Perceiving visual expansion without optic flow". Nature . 410 (6830): 816–819. Bibcode:2001Natur.410..816S. doi:10.1038/35071075. PMID   11298449. S2CID   4406675. 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.
130. Melvyn A. Goodale (July 1, 2011). "Transforming vision into action". Vision Research. 51 (13): 1567–1587. doi:. ISSN   0042-6989. PMID   20691202.
131. "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.
132. "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.
133. "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.
134. "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.
135. 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.
136. "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.
137. 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.