Stopping Distances

 

How to Calculate Thinking, Braking & Overall Stopping Distances

A common question asked is how to remember thinking, braking and overall stopping distances.  Rather than remembering a list of the distances, you can calculate them instead using the method detailed below.  This method works for calculating the distances in feet.  You can convert back to metres afterwards if necessary.

 

Overall Stopping Distance (on dry roads)
The overall stopping distance is built from

 

• the thinking distance, i.e. the distance the vehicle has travelled in the time taken to react to a hazard; and

• the braking distance, i.e. the distance travelled from the moment the brakes of the vehicle are applied to the point when the vehicle comes to a complete stop.

 

The list below applies a 'factor', dependent on the speed you are travelling, which is multiplied with the speed to calculate the overall stopping distance in feet.

Speed (mph)

Factor

Overall stopping distance (ft)
(speed x factor)

20 x 2 =      40

30 x 2.5 =   75

40 x 3 =      120

50 x 3.5 =   175

60 x 4 =      240

70 x 4.5 =   315

 

The factors are easy to remember - just start at 2 for 20mph and add 0.5 for each 10mph increase in speed.

 

Converting feet to metres

If you want to calculate stopping distances in metres instead of feet, simply do the calculations in feet and then convert the final answer back to metres: 1 foot = 0.3048 metres, or, to ease calculation, 1 foot is roughly equal to 3/10 metres, i.e. divide the distance by 10 and multiply by 3