Stopping Distances

The distance a vehicle takes to stop is split into two parts: Thinking Distance and Braking distance.

Thinking time is defined as the time it takes from seeing a need to stop and actually applying the brakes. The thinking distance is the amount of ground covered in this time.

Braking time is defined as the amount of time it takes to stop once the brakes have been applied. The braking distance is the amount of ground covered with the brakes on.

The bigger the mass of a vehicle, the the braking distance is, ie a lorry takes to stop than a car.

The bigger the applied braking force, the the braking distance is, unless it causes .

The braking distance is decreased when the speed of the vehicle is .

Braking distance also depends on the condition of the vehicle (eg worn brakes) and weather / road conditions.

Thinking time is affected by the driver's reaction time which is affected by, amongst other things, , and .

In the highway code (which you will be tested on for your driving license) the following typical figures are given.

20 MPH
	6 metres	6 metres	= 12 metres
30 MPH
	9 metres	14 metres	= 23 metres
40 MPH
	12 metres     24 metres		= 36 metres
50 MPH
	15 metres     38 metres		= 53 metres
60 MPH
	18 metres     55 metres		= 73 metres
70 MPH
	21 metres     75 metres		= 96 metres
Thinking Distance
Braking Distance
average car length = 4 metres

A good rule of thumb is 'the two second rule'. This states that you should always be at least 2 seconds behind the car in front, 4 seconds in poor weather.