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Braking distance refers to the distance a vehicle will travel from the point when its brakes are fully applied to when it comes to a complete stop. It is primarily affected by the original speed of the vehicle and the coefficient of friction between the tires and the road surface, [Note 1] and negligibly by the tires' rolling resistance and vehicle's air drag.
Extra time should be added for wet, rainy, slippery, foggy or other weather situations accordingly. [8] For heavy duty commercial vehicles it is recommended 4-6 seconds following distance for speeds under 30 mi/h (48 km/h), and 6-8 seconds following distance for speeds over 30 mi/h (48 km/h). [ 9 ]
The three second rule is a time for the defensive driver to judge the minimum safe trailing distance to help avoid collisions under ideal driving conditions. The red car's driver picks a tree to judge a two-second safety buffer. The two-second rule is a rule of thumb by which a driver may maintain a safe trailing distance at any speed.
A generous amount of time is given for the perception-reaction process, and a fairly low rate of deceleration is used. The design sight distance allows a below-average driver to stop in time to avoid a collision in most cases. Driver perception/reaction distance is calculated by: d PRT = 0.278 Vt (metric) d PRT = 1.47 Vt (US customary) Where:
A vehicle accelerating from a stop travels this distance in time t i = √ 2d i ⁄ a i while through traffic travels a distance equal to their speed multiplied by that time. The time t pc , 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 ...
Headway is the distance or duration between vehicles in a transit system. The minimum headway is the shortest such distance or time achievable by a system without a reduction in the speed of vehicles. The precise definition varies depending on the application, but it is most commonly measured as the distance from the tip (front end) of one ...