Stopping Distances - RoSPA's Pedestrian Injury Simulator

Speed and Stopping Distances

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Drivers who travel at higher speeds have less time to identify and react to what is happening around them. It takes them longer to stop. And if there is a crash, it is more severe, causing greater injury to the occupants and any pedestrian or rider they hit.

A car’s overall stopping distance is made up of the driver’s thinking distance (the distance the car travels from the point when the driver realises they need to brake and they actually start to brake) and their braking distance (the distance the car travels from the point when the driver starts to press the brake pedal and the vehicle comes to a complete stop).

Speed increases both the thinking distance and the braking distance. At faster speeds, the driver will cover more ground before reacting to a hazard and more distance before the driver brakes to a complete stop.

Speeding causes thousands of serious crashes and injuries every year.

Inappropriate speed contributes to around 10% of all injury collisions reported to the police, 13% of crashes resulting in a serious injury and 24% of collisions which result in a death. This includes exceeding the speed limit but also driving or riding within the speed limit but too fast for the conditions (for example, in poor weather, poor visibility or high pedestrian activity).

In 2014, 282 people were killed in crashes involving someone exceeding the speed limit and a further 126 people died when someone was travelling too fast for the conditions.

Approximately two-thirds of all crashes in which people are killed or injured happen on roads with a speed limit of 30 mph or less.

The risk of a pedestrian being killed if they are hit by a car increases as the car’s speed increases. A pedestrian who is hit by a car travelling at between 30 mph and 40 mph is between 3.5 and 5.5 times more likely to be killed than if hit by a car travelling at below 30 mph.

The Simulator and Speed

The simulator allows you to compare the potential effects of driving at different speeds on a 30 mph residential street, and shows how your choice of speed increases your stopping distance, and the chances of hitting a pedestrian who is crossing the road.

The time it takes the driver to respond (the thinking time) is the same, but the distance the car covers during this thinking time increases at higher speeds.

The car’s braking distance also increases as speed increases, with even a relatively small increase in speed increasing the braking distance substantially. For example, the simulator illustrates that if the speed is doubled then the braking distance increases by four times. This makes it much more likely that the driver will hit the pedestrian rather than stop before reaching them.

Top Ten Tips to Avoid Speeding

Many drivers unintentionally exceed the speed limit, often without realising it. Modern cars are so powerful and comfortable they give drivers little sensation of their speed – it can be easy to creep above the limit.

Whether intentionally or not, exceeding the speed limit is illegal and can be very dangerous, especially in 20mph or 30mph zones where even a couple of miles per hour extra may be the difference between a pedestrian walking away or suffering a serious injury.

Some simple and practical tips to make it easier to stay within speed limits:

  1. Check your speedometer regularly, especially when leaving high speed roads
  2. Know the limits – look for signs, especially at junctions
  3. Assume lamp posts mean 30 mph, until signs say otherwise, but remember it could be 20 mph
  4. Remember, speed limits are a maximum, not a target
  5. 20’s plenty when kids are about – and may even be too fast
  6. Try no higher than 3rd gear in a 30 mph limit
  7. Recognise what makes you speed - keeping up with traffic, overtaking or being tailgated
  8. Concentrate – distracted drivers speed
  9. Slow down when entering villages
  10. Give yourself time – there’s no need to speed and you won’t get there quicker


“Reported Road Casualties Great Britain, 2014”, Department for Transport,  2015,

“Inappropriate Speed Factsheet”, RoSPA, 2015

Top Ten Tips to Avoid Speeding”, RoSPA, 2011

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Produced with the support of the Department for Transport.
Produced with the support of the Department for Transport.
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