Understanding Stopping Distances
How far will your car travel from the moment you spot a hazard until you bring your car to a complete stop? The distance can vary depending on the car you drive, your reaction times, the standard of maintenance of your brakes, and the road conditions. Very often, however, the stopping distance is longer than drivers think.
It is also important to note that stopping distance is not the same as braking distance – braking distance is the time it takes your car to stop once you apply the brakes.
Two things, however, impact on stopping distance:
- Your reaction time
- The time it then takes the car to stop once you react
Reaction time includes the time it takes for you to realise there is a hazard in front of you as well as the physical time it takes for you to apply the brake. This can be impacted by a range of factors including your concentration levels and how tired you are. Alcohol also slows reaction times.
What about average reaction times? In most situations, reaction times are fast, but your car can still travel a considerable distance before you get your foot on the brake. For example, a typical reaction time is normally less than one second – often around two-thirds of a second. How does this translate to distance, though? If you’re travelling at 100 km/h your car will travel over 18 metres from the moment you see a hazard until your foot gets on the brake.
Modern cars fitted with automatic braking systems mean reaction times are not as important in some situations as the car takes on the responsibility of applying the brakes.
Once you get your foot on the brake, several additional factors impact on the distance it takes your car to stop. This includes the quality of the braking system in your car as well as the physical condition of your brakes. Your tyres are also important – grip, tread level, and tyre pressure. The weight of your car can also impact braking distance.
One of the most significant factors that determines braking distance, however, is the surface of the road. Slippery road conditions, such as when it is wet, can increase the braking distance of your car by 75 percent and more. This means your braking distance will be about 45 metres longer when travelling at 100 km/h in wet conditions compared to dry. In the snow or ice, it will be even longer again – considerably longer.
The below table shows the overall stopping distance combining both your reaction time and your car’s braking distance:
- At 30 km/h – 10.8 metres in the dry and 14.9 metres in the wet
- At 50 km/h – 24.0 metres in the dry and 35.2 metres in the wet
- At 60 km/h – 32.4 metres in the dry and 48.5 metres in the wet
- At 80 km/h – 52.7 metres in the dry and 81.4 metres in the wet
- At 100 km/h – 77.7 metres in the dry and 122.6 metres in the wet
- At 120 km/h – 107.5 metres in the dry and 172.2 metres in the wet
One thing to note from these figures is your stopping distance doesn’t just double when your speed doubles – it increases by considerably more. For example, your stopping distance is three times longer at 60 km/h compared to 30 km/h.
Keeping a Safe Stopping Distance
The table above shows the importance of keeping a safe distance from the car in front of you. One good guide to follow is the two-second rule. This involves selecting a stationary object and then counting in seconds once the car in front of you passes it. You should be at least two seconds behind in perfect conditions (on a dry road surface with good quality tyres and well-maintained brakes). Leave an even greater distance behind the car in front of you if the conditions aren’t perfect.
Finally, stay alert to what is happening on the road by looking well ahead. This will give you more time to stop.