stopping distances

Back to SCIENCE main page

The stopping distance of a car depends on two things: the thinking distance and the braking distance. Several factors influence the thinking distance and the braking distance, and can increase the overall stopping distance.

Thinking distance

It takes a certain amount of time for a driver to react to a hazard and to start applying the brakes. During this time, the car is still moving. The faster the car is travelling, the greater this thinking distance will be.

The thinking distance will also increase if the driver's reactions are slower because the driver is:

  • Under the influence of alcohol.
  • Under the influence of drugs.
  • Tired

Braking distance

The braking distance is the distance the car travels from where the brakes are first applied to where the car stops. If the braking force is too great, the tyres may not grip the road sufficiently and the car may skid. The faster the car is travelling, the greater the braking distance will be

The braking distance will also increase if:

  • The brakes or tyres are worn.
  • The weather conditions are poor, such as icy or wet roads.
  • The car is more heavily laden, for example with passengers and luggage.

Graph of stopping distancesStopping distance

The stopping distance is the thinking distance plus the braking distance.

The graph shows some typical stopping distances. The thinking distance is in red, the braking distance is in green and the overall stoppinng distance is in blue.


[ This page has been adapted from ]