Do you know your Highway Code?
Bringing your car to a complete halt takes time. It takes time for you to react to a braking situation, and it takes time for your car to respond to your braking actions. While it is true that advances in brake technology make it easier to stop more quickly and safely than ever before, factors such as weather and road conditions, along with the condition of your tyres can greatly affect your actual stopping distance.
Typical stopping distances according to the Highway Code
The Highway Code publishes a guide to typical stopping distances for cars from different speeds. In dry weather on a standard road surface it is expected that a car travelling at 20mph will take 12 metres or 3 car lengths to come to a standstill. This is made up of 6 metres thinking and reaction time, plus a further 6 metres of braking time.
For other speeds stopping distances are as follows:
- 30mph - 9 metres thinking & reaction time + 14 metres braking time.
Total 23 metres (6 car lengths)
- 40mph - 12 metres thinking & reaction time + 24 metres braking time.
Total 36 metres (9 car lengths)
- 50mph - 15 metres thinking & reaction time + 38 metres braking time.
Total 53 metres (13 car lengths)
- 60mph - 18 metres thinking & reaction time + 55 metres braking time.
Total 73 metres (18 car lengths)
- 70mph - 21 metres thinking & reaction time + 75 metres braking time.
Total 96 metres (24 car lengths)
In wet conditions these distances are doubled. To stop from 50mph on a wet road it'll take you almost the entire length of a full-size football pitch to come to a complete halt. On an icy road stopping distances should be multiplied by a factor of 10!
The depth of your tyre tread has a significant impact on stopping distances. New tyres are typically supplied with a tread depth of about 8mm. A partly worn tyre that is reduced to 5mm of tread depth increases your stopping distance by about 14%. At a tread depth of 3mm that margin goes up to 30%, and on the legal limit of 1.6mm it adds as much as 60% to your actual stopping distance.