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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.
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 .
The two-second rule is useful as it can be applied to any speed. Drivers can find it difficult to estimate the correct distance from the car in front, let alone remember the stopping distances that are required for a given speed, or to compute the equation on the fly. The two-second rule provides a simpler way of perceiving the distance.
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]
Right before a wheel locks up, it will experience a rapid deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It might take a car two to four seconds to stop from 60 mph (96.6 km/h) under ideal conditions, but a wheel that locks up could stop spinning in less than a second.
The Official Highway Code, 17th edition cover, 2022. The Highway Code is the official set of information and guidance for road users in the United Kingdom.Its objective is to promote the safe and efficient use of the road network.
A non-primary road sign near Bristol shows Guildford Rules patches.Road signs in the United Kingdom and in its associated Crown dependencies and overseas territories conform broadly to European design norms, with a number of exceptions: direction signs omit European route numbers, and road signs generally use the imperial system of units (miles and yards), unlike the rest of Europe (kilometres ...
Actual stopping distances are also affected by road conditions, the mass of the car, the incline of the road, and numerous other factors. For design, a conservative distance is needed to allow a vehicle traveling at design speed to stop before reaching a stationary object in its path.