Understanding Stopping Distances When Driving
Knowing how to work out stopping distances is one of the most important safety skills for any driver. Stopping distance is the total distance your vehicle travels from the moment you notice a hazard to the moment your vehicle comes to a complete stop. Understanding how this works helps drivers judge safe following distances and avoid collisions.
Stopping distance is made up of two key parts: thinking distance and braking distance.
1. Thinking Distance
Thinking distance is the distance your vehicle travels between noticing a hazard and pressing the brake pedal.
Even if you react quickly, your brain still needs a fraction of a second to recognise danger and send a signal to your foot to press the brake.
A simple rule is that thinking distance increases directly with speed.
For example:
Speed
Thinking Distance
20 mph
6 metres
30 mph
9 metres
40 mph
12 metres
50 mph
15 metres
60 mph
18 metres
70 mph
21 metres
If you double your speed, your thinking distance roughly doubles as well.
Factors that can increase thinking distance include:
• Tiredness
• Alcohol or drugs
• Distractions such as phones
• Poor visibility
2. Braking Distance
Braking distance is the distance your vehicle travels after you press the brakes until the car stops completely.
This distance increases much faster with speed because the vehicle has more momentum.
Typical braking distances are:
Speed
Braking Distance
20 mph
6 metres
30 mph
14 metres
40 mph
24 metres
50 mph
38 metres
60 mph
55 metres
70 mph
75 metres
Unlike thinking distance, braking distance increases exponentially with speed. This means that doubling your speed can more than quadruple the braking distance.
3. Total Stopping Distance
Total stopping distance is simply:
Thinking Distance + Braking Distance
For example:
At 30 mph
Thinking distance = 9 metres
Braking distance = 14 metres
Total stopping distance = 23 metres
Here are the typical stopping distances used in the UK Highway Code:
Speed
Total Stopping Distance
20 mph
12 metres
30 mph
23 metres
40 mph
36 metres
50 mph
53 metres
60 mph
73 metres
70 mph
96 metres
4. Conditions That Increase Stopping Distance
Stopping distances can increase significantly depending on road and vehicle conditions.
Wet roads can double braking distance.
Ice or snow can increase stopping distance up to ten times.
Other factors include:
• Worn tyres
• Poor brakes
• Heavy vehicle load
• Downhill roads
• Loose gravel or mud
Because of these risks, drivers should always leave extra space between vehicles in bad weather.
5. The Two Second Rule
A simple way to maintain a safe distance while driving is the two second rule.
Choose a fixed object such as a road sign. When the vehicle in front passes it, start counting:
“Only a fool breaks the two second rule.”
If you pass the object before finishing the phrase, you are driving too close and should slow down.
In wet weather, increase this to four seconds.
Final Thoughts
Understanding stopping distances is not just something for a driving test. It is essential knowledge that can prevent accidents and save lives. By remembering that stopping distance is made up of thinking distance and braking distance, and by adjusting your driving for speed and road conditions, you can drive more safely and responsibly.
Always leave enough space, stay alert, and remember that the faster you travel, the longer it takes to stop.
Official DVSA Learning to Drive Book
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