Stopping (Braking) Distance

The energy that has to be dissipated to stop a car, called kinetic energy, increases exponentially as the square of speed. So the difference between 30 and 35mph is only a 16 per cent increase in speed, but it's a 36 per cent increase in kinetic energy, which is one of the key factors in stopping distance.

Stopping distance is affected by a number of factors, including load, condition of the road surface, tyres, brakes, driver skill and design and type of vehicle.

It doesn't matter how good a car's engineering and brakes are, there is nothing they can do to contradict the laws of physics. This increase in speed will inevitably increase stopping distance.

These figures assume dry weather and good tyres and an average family saloon. Naturally, stopping distances will vary according to weather conditions, and some cars may perform in different ways. But we want drivers to recognise that however good a driver they think they are and however good their car is, the difference between driving at 30 and driving a few mph over the limit, will lead to a much longer stopping distance that could lead to drastic consequences.

Speed Thinking Distance Braking Distance Total Stopping Distance
20 mph 1.5 car lengths 1.5 car lengths 3 car lengths
30 mph 2.5 car lengths 3.5 car lengths 6 car lengths
40 mph 3 car lengths 6 car lengths 9 car lengths
50 mph 3.5 car lengths 9.5 car lengths 13 car lengths
60 mph 4.5 car lengths 13.5 car lengths 18 car lengths
70 mph 5 car lengths 19 car lengths 24 car lengths