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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.
d MT = braking distance, m (ft) V = design speed, km/h (mph) a = deceleration rate, m/s 2 (ft/s 2) Actual braking distances are affected by the vehicle type and condition, the incline of the road, the available traction, and numerous other factors. A deceleration rate of 3.4 m/s 2 (11.2 ft/s 2) is used to determine stopping sight distance. [6]
See Table of 2-second following distances. Critical speed ... Now, the total stopping distance is the sum of the braking and perception-reaction distances:
The rule is not a guide to safe stopping distance, it is more a guide to reaction times. The two-second rule tells a defensive driver the minimum distance needed to reduce the risk of collision under ideal driving conditions. The allotted two-seconds is a safety buffer, to allow the following driver time to respond.
The stopping sight distance table isn't intended to represent a real vehicle. The deceleration rate was obtained by measuring drivers, not vehicles. It was found that most drivers will brake at a rate of at least 11.2 ft/s 2. Almost all modern vehicles can exceed this rate, but for design purposes, it makes sense to be conservative.--
British Railway Class 90 infobox showing brake force Brake force to weight ratio of the Class 67 is higher than some other locomotives. In the case of railways, it is important that staff are aware of the brake force of a train so sufficient brake power will be available to bring the train to a halt within the required distance from a given speed.
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While a corner sight distance which far exceed the braking distance at the design speed should be afforded to the driver, he or she is still generally required to maintain such control and safe speed as to be able to stop within the assured clear distance ahead (ACDA), [28] [29] [30] and the basic speed rule always applies. Jurisdictions often ...