Assured clear distance ahead

In legal terminology, the assured clear distance ahead (ACDA) is the distance ahead of any terrestrial locomotive device such as a land vehicle, typically an automobile, or watercraft, within which they should be able to bring the device to a halt.^[1] It is one of the most fundamental principles governing ordinary care and the duty of care for all methods of conveyance, and is frequently used to determine if a driver is in proper control and is a nearly universally implicit consideration in vehicular accident liability.^[2]^[3]^[4] The rule is a precautionary trivial burden required to avert the great probable gravity of precious life loss and momentous damage.^[5]^[6]^[7] Satisfying the ACDA rule is necessary but not sufficient to comply with the more generalized basic speed law, and accordingly, it may be used as both a layman's criterion and judicial test for courts to use in determining if a particular speed is negligent, but not to prove it is safe.^[8] As a spatial standard of care, it also serves as required explicit and fair notice of prohibited conduct so unsafe speed laws are not void for vagueness.^[9]^[10]^[11] The concept has transcended into accident reconstruction and engineering.^[12]

This distance is typically both determined and constrained by the proximate edge of clear visibility, but it may be attenuated to a margin of which beyond hazards may reasonably be expected to spontaneously appear. The rule is the specific spatial case of the common law basic speed rule,^[13] and an application of volenti non fit injuria. The two-second rule may be the limiting factor governing the ACDA, when the speed of forward traffic is what limits the basic safe speed, and a primary hazard of collision could result from following any closer.^[2]^[3]

As the original common law driving rule preceding statutized traffic law,^[13] it is an ever important foundational rule in today's complex driving environment. Because there are now protected classes of roadway users—such as a school bus, mail carrier, emergency vehicle, horse-drawn vehicle, agricultural machinery, street sweeper, disabled vehicle,^[14] cyclist, and pedestrian—as well as natural hazards which may occupy or obstruct the roadway beyond the edge of visibility,^[14] negligence may not depend ex post facto on what a driver happened to hit, could not have known, but had a concurrent duty to avoid.^[13]^[15] Furthermore, modern knowledge of human factors has revealed physiological limitations—such as the subtended angular velocity detection threshold (SAVT)—which may make it difficult, and in some circumstance impossible, for other drivers to always comply with right-of-way statutes by staying clear of roadway.^[16]^[17]

^ Cite error: The named reference CDLM was invoked but never defined (see the help page).
^ ^a ^b 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.
^ ^a ^b 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.
^ 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. Vol. 75. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 327.
^ Cite error: The named reference Newton was invoked but never defined (see the help page).
^ Cite error: The named reference Kloeden et. al. was invoked but never defined (see the help page).
^ Benjamin Preston (January 8, 2016). "Insurers Brace for a Self-Driving Future (and a Fading Need for Insurance)". The New York Times. p. B3.
^ 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
^ Cite error: The named reference 269 US 385 was invoked but never defined (see the help page).
^ Cite error: The named reference 1998 MT 321 was invoked but never defined (see the help page).
^ Cite error: The named reference void for vagueness was invoked but never defined (see the help page).
^ Cite error: The named reference :0 was invoked but never defined (see the help page).
^ ^a ^b ^c Cite error: The named reference 189 Cal. 335 was invoked but never defined (see the help page).
^ ^a ^b Cite error: The named reference 235 N.C. 568 was invoked but never defined (see the help page).
^ Cite error: The named reference 100 Cal. App. 2d 411 was invoked but never defined (see the help page).
^ Cite error: The named reference Hoffmann & Mortimer was invoked but never defined (see the help page).
^ Cite error: The named reference Maddox was invoked but never defined (see the help page).

[CDLM-1] Cite error: The named reference CDLM was invoked but never defined (see the help page).

[NY_Jur-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.

[Leibowitz&Herschel-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.

[75_ALR.3d_327-4] 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. Vol. 75. The Lawyers Co-operative Publishing Company; Bancroft-Whitney; West Group Annotation Company. p. 327.

[Newton-5] Cite error: The named reference Newton was invoked but never defined (see the help page).

[Kloeden_et._al.-6] Cite error: The named reference Kloeden et. al. was invoked but never defined (see the help page).

[material_cost_of_accidents-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

[269_US_385-9] Cite error: The named reference 269 US 385 was invoked but never defined (see the help page).

[1998_MT_321-10] Cite error: The named reference 1998 MT 321 was invoked but never defined (see the help page).

[void_for_vagueness-11] Cite error: The named reference void for vagueness was invoked but never defined (see the help page).

[:0-12] Cite error: The named reference :0 was invoked but never defined (see the help page).

[189_Cal._335-13] Cite error: The named reference 189 Cal. 335 was invoked but never defined (see the help page).

[235_N.C._568-14] Cite error: The named reference 235 N.C. 568 was invoked but never defined (see the help page).

[100_Cal._App._2d_411-15] Cite error: The named reference 100 Cal. App. 2d 411 was invoked but never defined (see the help page).

[Hoffmann_&_Mortimer-16] Cite error: The named reference Hoffmann & Mortimer was invoked but never defined (see the help page).

[Maddox-17] Cite error: The named reference Maddox was invoked but never defined (see the help page).

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