Stopping a vehicle

The total distance needed to stop a car is not just the distance the car travels after the brakes have been applied, called the braking distance. There is also the time needed for the driver to react to the reason for the braking. For example when the driver sees an animal jump out into the road, his brain needs to process the visual information and his muscles need to move his foot from the accelerator to the brake. This is called the reaction time. During the reaction time, the car will have travelled a certain distance called the thinking distance. So the total stopping distance is made up of the thinking distance and the braking distance.

Total stopping distance = Thinking distance + Braking distance It is obvious that the braking distance is longer at higher speeds but the thinking distance is also longer at higher speeds. Under normal conditions a driver’s reaction time will be the same for any given speed, but in that time a car going faster will have travelled a further distance.

The Highway Code gives example stopping distances under normal conditions.