Drivers Fact Sheets

The Mathematics Of Speed

Slowing Down In Towns And Villages

Let us take a look at the maths involved in not observing the speed limit.

A simple rule: The faster you drive, the less time you have to react and the harder you hit.

Result: Hit by a car at 40mph, 15% of pedestrians will survive.

Hit by a car at 20mph, 95% of pedestrians will survive.

Fact: 58% of drivers do not observe the 30mph speed limit

Consequence: Hit at 35mph rather than 30mph a pedestrian is two and a half times more likely to die.

Why: The force of the impact increases by more than a third.

The Result: 69% of all crashes resulting in death or injury and 40% of all deaths on the road happen on roads in built up areas, many of which have speed limits of 30mph or less.

Driver and front seat passengers: It is not only pedestrians and cyclists who are at risk but also you and your passengers.  If you are sat in the front seat of a car and belted up you are three times more likely to suffer injury in a crash at 30mph than 20mph.

Stopping Distances: Stopping distances include the time it takes to spot a hazard and for your mind to process the information (‘thinking distance’) and the time it takes to actually stop (‘braking distance’)

Thinking distance increases in direct proportion to speed but braking distance increases at a much faster rate, actually it increases in proportion to the speed squared. This is because the amount of kinetic energy (the pressure on the brakes) required to bring the vehicle to a stop increases exponentially as the speed increases.

For example, if you are driving a car and increase your speed by 50% from 20mph to 30mph, your thinking distance will increase by 50% from 6 metres to 9 metres. But your braking distance will increase by 134% from 6 metres to 14 metres. This means that your total stopping distance almost doubles increasing from 12 to almost 23 metres, a matter of life and death.

Child Pedestrians:  Britain has one of the worst child pedestrian death rates in Europe. Try and keep to 20mph around school and residential areas.

Staying within the Limit to protect children: Imagine two cars, travelling side by side, one at 30mph and one at 35mph.  A child runs into the road 22 metres ahead.  The two drivers brake. What happens?

Assuming the child fails to spot the oncoming cars and move out of the way in time, the 30mph car will nevertheless be able to stop with less than half a metre to spare before reaching the child.  The car doing 35mph will not stop in time.  It will hit the child at a speed of 20mph.  At this speed, the child could well be seriously injured.  There is a one in twenty chance they will die

Conclusion: Best Advice

To drive at safe speeds in towns and villages you should:

Watch Out For Speed Limit Signs

Repeater signs are not common in 30mph zones, and some signs may be small or covered by mud or foliage.

Check Your Speedometer Regularly

It only takes a fraction of a second and should be as automatic as checking your mirrors. Remember that breaking limits by just a few miles per hour can be fatal.

Use Your Gears

As you approach a 20mph or 30mph zone from a higher limit road, switch to third gear.  If you are driving on a 20mph or 30mph road and are travelling downhill, switch to a lower gear to stop you unwittingly picking up speed.

Drive Well Under Limits, Not At Them

Especially when pedestrians and cyclists are about.  Make sure you do not let your speed creep up.

If You Have To Use Certain Roads At Dangerous Times

Such as school opening and closing times and pub closing times, take extra care.

Keep Your Distance

Keep at least a two-second gap between you and the vehicle in front on all types of roads.

Drive As Though There Is A Hazard

Such as a child running into the road, around every corner.  That means slowing down when your view of the road ahead is restricted in any way.

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I confirm I have read the fact sheet ‘The Mathematics Of Speed.’

Signed……………………………………………………………Date……………………………………………

Name of Driver……………………………………………………Vehicle Reg…………………………………..