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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]
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] Rear-end collisions are the number one type of traffic collisions .
economics, range greater is better (mpg and km/L), lower is better (L/100 km) must be specified on new vehicles for sale in the US and UK Maximum g-force(s) g or ft/s 2: g or ft/s 2: g or m/s 2: acceleration, braking (safety) higher is usually better measures cornering, braking or forward acceleration Ground pressure: psi: psi: pascals ...
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 ...
On the M25 for example, distances are referenced to a point near Junction 31 even though the section of the ring road between Junction 31 (post 186.6) and Junction 1a (post 5.7) is the A282, not the M25. [3] On motorways distance marker posts also bear an arrow pointing towards the location of the nearest emergency telephone. [4]
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.
In the case of automobile traffic, the key consideration in braking performance is the user's reaction time. [6] Unlike the train case, the stopping distance is generally much shorter than the spotting distance. That means that the driver will be matching their speed to the vehicle in front before they reach it, eliminating the "brick-wall" effect.