In legal terminology, the assured clear distance ahead (ACDA) is the distance ahead of any terrestrial locomotive device such as a land vehicle, typically an automobile, or watercraft, within which they should be able to bring the device to a halt.[1] It is one of the most fundamental principles governing ordinary care and the duty of care for all methods of conveyance, and is frequently used to determine if a driver is in proper control and is a nearly universally implicit consideration in vehicular accident liability.[2][3][4] The rule is a precautionary trivial burden required to avert the great probable gravity of precious life loss and momentous damage.[5][6][7] Satisfying the ACDA rule is necessary but not sufficient to comply with the more generalized basic speed law, and accordingly, it may be used as both a layman's criterion and judicial test for courts to use in determining if a particular speed is negligent, but not to prove it is safe.[8] As a spatial standard of care, it also serves as required explicit and fair notice of prohibited conduct so unsafe speed laws are not void for vagueness.[9][10][11] The concept has transcended into accident reconstruction and engineering.[12]
This distance is typically both determined and constrained by the proximate edge of clear visibility, but it may be attenuated to a margin of which beyond hazards may reasonably be expected to spontaneously appear. The rule is the specific spatial case of the common law basic speed rule,[13] and an application of volenti non fit injuria. The two-second rule may be the limiting factor governing the ACDA, when the speed of forward traffic is what limits the basic safe speed, and a primary hazard of collision could result from following any closer.[2][3]
As the original common law driving rule preceding statutized traffic law,[13] it is an ever important foundational rule in today's complex driving environment. Because there are now protected classes of roadway users–such as a school bus, mail carrier, emergency vehicle, horse-drawn vehicle, agricultural machinery, street sweeper, disabled vehicle,[14] cyclist, and pedestrian–as well as natural hazards which may occupy or obstruct the roadway beyond the edge of visibility,[14] negligence may not depend ex post facto on what a driver happened to hit, could not have known, but had a concurrent duty to avoid.[13][15] Furthermore, modern knowledge of human factors has revealed physiological limitations–such as the subtended angular velocity detection threshold (SAVT)–which may make it difficult, and in some circumstance impossible, for other drivers to always comply with right-of-way statutes by staying clear of roadway.[16][17]
As common law rule or statute
Determining the ACDA
ACDA rule-specific case generalized to the Basic Speed Law
Safe speed
"Assurance" beyond proximate edge of clear visibility as transference of liability
Derivations
Tables of reference constants and safe speeds
See also
Notes
References
pa follow at pa brainlest na den
