Stopping distances made simple

Stopping distances made simple
A car’s stopping distance is an important part of any learner driver’s theory test – but it’s also something we all-too-soon forget.

Following too closely to other cars – known as tailgating – is one of the biggest causes of road accidents in the UK and it could result in failing your driving test too.

Whether you're new to driving or have years of experience, knowing your stopping distances is a crucial part of staying safe on the roads, here we'll explain what they are, what affects them and how best to remember them.

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What are average stopping distances?

It's first worth noting that a stopping distance = thinking distance + braking distance.

The following stopping distances relate to an average sized family car in normal weather conditions, however, it is also worth mentioning that a number of other factors can affect the stopping distance of a car (which we have outlined below). 

 

Stopping distances

Unsurprisingly, the faster a car is travelling, the longer it takes to stop.

Travelling at 40mph rather than 30mph means it’ll take an extra 13 metres (more than three car lengths) to come to a stop – think about that next time you consider breaking the 30mph speed limit.

Stopping distances are can be split into two main categories: the thinking distance and the braking distance.

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What is thinking distance?

Both categories are pretty self-explanatory. The ‘thinking distance’ is how long it takes for the driver to react to a hazard and apply the brake.

At higher speeds, the car will cover a greater distance while the driver realises he or she needs to brake to avoid a hazard. The Highway Code provides the following thinking distances at different speeds:

SpeedThinking distance (before reacting)
20mph6 metres
30mph9 metres
40mph12 metres
50mph15 metres
60mph18 metres
70mph21 metres

At motorway speeds, you could cover the length of four cars before you even apply the brakes.

There are a number of factors that could affect a driver’s thinking distance. We’ll come onto those shortly.

What is braking distance?

The second part of the overall stopping distance is made up of the braking distance. This is how far your car travels while you’ve got your foot on the brake attempting to bring it to an emergency stop.

These are the official braking distances provided by the Highway Code:

SpeedBraking distance
20mph6 metres
30mph14 metres
40mph24 metres
50mph38 metres
60mph55 metres
70mph75 metres

At 20mph, the braking distance is exactly the same as the thinking distance. These combine to provide a total stopping distance of 12 metres.

At 70mph, the 75-metre braking distance makes up nearly 80% of the overall 96-metre stopping distance.

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Techniques to remember stopping distances

Stopping distances are a favourite part of the theory test, but they’re not easy to remember. That’s unless you know a special trick… which we’ll reveal here.

It takes a bit of maths, but bear with us. All you need to do is multiply the speed by intervals of 0.5, starting with 2. That’ll give you the stopping distance in feet, which is acceptable for the theory test. For example…

20mph x 2 = 40 feet

30mph x 2.5 = 75 feet

40mph x 3 = 120 feet

50mph x 3.5 = 175 feet

60mph x 4 = 240 feet

70mph x 4.5 = 315 feet

There are 3.3 feet in a metre – so divide the distance in feet by 3.3 to get the stopping distance in metres. You’ll need a calculator for that, but it shouldn’t be necessary for the theory test.

What other factors affect stopping distances?

As we’ve already mentioned, stopping distances can be influenced by a number of factors.

Some people suggest the stopping distances in the Highway Code are out of date because modern cars, with ABS systems and better tyres, can stop a lot quicker.

Stopping distance

But remember, factors like this will only affect the braking distance. Unless the car’s fitted with an automatic emergency braking system, it won’t reduce the thinking time.

1. Weather

In poor weather conditions, a car’s total stopping distance is likely to be longer for a number of reasons. For a start, poor visibility might mean the driver takes longer to react – increasing his/her thinking distance. But slippery roads caused by rain, snow or ice will also extend the braking distance.

Research suggests braking distances can be doubled in wet conditions – and multiplied by 10 on snow or ice. That means, in the snow, it could take you further than the length of seven football pitches to stop from 70mph.

For help tackling the conditions check out our winter driving guide.

2. Road condition

It’s not always as obvious as ‘bad weather equals long stopping distances’, either. A road might be particularly greasy if there has been rain after a period of hot weather, or if oil has been spilt on it.

Be prepared for black ice on cold days, and watch out for loose surfaces such as gravel. All these could make it difficult to stop in a hurry.

READ MORE: How to drive an automatic

3. Driver condition

While all these factors can affect the braking distance, the individual behind the wheel is responsible for the thinking distance – and that can have a huge effect on the overall stopping distance.

A driver’s age, how awake they are and if they’ve consumed any drugs or alcohol can all influence how quickly it takes them to react.

Using a mobile phone rather than concentrating on the road can have devastating effects on a driver’s stopping distance – just a few seconds glancing at your phone can add an football pitch to your overall stopping distance at motorway speeds. If the traffic ahead has stopped, that could ruin your day very quickly.

Other distractions in the car – such as loud music and passengers – can also affect the thinking time before you apply the brakes.

4. Car condition

While many modern cars may indeed be able to stop in shorter distances than the official Highway Code states, a car’s condition can also have an impact.

For example, cars equipped with budget tyres can take an extra 14 metres to stop from 70mph in wet conditions compared to cars with ‘premium brand’ tyres, or five metres in the dry.

Research has also found that tyres on the legal limit of 1.6mm tread can need an extra 60% more road to stop compared to brand new tyres.

Under-inflated tyres will also have an impact on stopping distances, as will cars with poorly maintained brakes.

Click here to find out more about the importance of tyre health and a video on how to health check your tyres.

Check your brake pads to make sure they have plenty of life left in them, and test your brakes after driving through water to check for moisture left between the pads and discs.

For more on brake pads read our definitive guide to looking after your brake pads

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