Typical stopping distances

It is important to be able to:

  • estimate how the stopping distance for a vehicle varies with different speeds
  • interpret graphs relating speed to stopping distance

The diagram shows some typical stopping distances for an average car in normal conditions.

Bar chart showing the thinking and braking distances of a car at different speeds. The greater the speed, the longer the thinking and braking takes.

Some typical stopping distances

Travelling at 20 mph (32 km/h):

  • thinking distance = 6 m
  • braking distance = 6 m
  • total stopping distance = 12 m

Travelling at 40 mph (64 km/h):

  • thinking distance = 12 m
  • braking distance = 24 m
  • total stopping distance = 36 m

Travelling at 70 mph (112 km/h):

  • thinking distance = 21 m
  • braking distance = 75 m
  • total stopping distance = 96 m

It is important to note that the thinking distance is proportional to the starting speed. This means that it increases proportionally as speed increases – ie if speed doubles, thinking distance also doubles. However, the braking distance increases by a factor of four each time the starting speed doubles.

For example, if a car doubles its speed from 30 mph to 60 mph, the thinking distance will double from 9 m to 18 m and the braking distance will increase by a factor of four from 14 m to 56 m.