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What are the correct UK stopping distances?

23rd December 2020

We have all been in the stressful driving scenario when the driver behind gets a bit too close, otherwise known as tailgating. Not only is this very stressful and dangerous for the driver in front, but tailgating is illegal in the UK. It’s important to understand how to calculate stopping distance and what might change it from day to day to avoid not only tailgating, but preventing a serious accident.

What is stopping distance?

Stopping distance is the total amount of time it takes for your vehicle to stop from the moment you first think about stopping to the second you come to a complete halt or take your foot of the brake. Stopping distance is calculated using this formula:

Thinking Distance + Braking Distance = Stopping Distance

Thinking distance is the distance travelled in the time that it takes you, as the driver, to realise you must brake in order to avoid a hazard directly ahead of you. For example, if the car in front of you suddenly braked, the thinking distance would be from the moment the car in front braked to the moment you start to break. According to the UK Highway Code, a car of around 4 metres in length can have thinking distance calculated like so:

Source: RAC

Braking distance begins from the moment you apply the brakes and ends as soon as you come to a stop or remove your foot from the brakes. The distance travelled during this time period is what is known as braking distance. If we take our example of the sudden braking once more, the braking distance would be captured from the second you braked to the second you stop. The Highway Code sets out braking distances based on a 4m car:

Source: RAC

How do I calculate stopping distance?

It is difficult to give a set formula beyond Thinking Distance + Braking Distance when it comes to calculating stopping distance. There are many different variants that determine the stopping distance of your vehicle including size of car, speed, weather and the driver's attention levels. The below calculations, however, are based on the average family-sized car driven by an attentive driver in good weather conditions.

Starting from 20mph, simply multiply 10mph speed intervals by 0.5, beginning with 2, for example, 2, 2.5, 3, 3.5 etc, as follows:

  • 20 mph x 2 = 40 feet (12 metres or 3 car lengths)
  • 30 mph x 2.5 = 75 feet (23 metres or 6 car lengths)
  • 40 mph x 3 = 120 feet (36.5 metres or 9 car lengths)
  • 50 mph x 3.5 = 175 feet (53 metres or 13 car lengths)
  • 60 mph x 4 = 240 feet (73 metres or 18 car lengths)
  • 70 mph x 4.5 = 315 feet (96 metres or 24 car lengths)

What can affect stopping distance?

Stopping distance is not the same every time you drive your car. There are a number of factors that can change every time you drive:

  • Poor weather conditions can increase your stopping time significantly potentially creating more accidents. Weather such as heavy rain or icy road conditions can cause braking to be slower due to the roads being more slippery. On extremely sunny days, poor visibility can be an issue – the light may blind you temporarily making it hard to see upcoming hazards and reducing potential thinking time.  
  • Road conditions will have a significant impact on stopping distances. Poor terrain, such as numerous potholes, can decrease stopping distance. On hot days, roads can become greasy which increases stopping distance. Understanding the road conditions you’re driving on is vital for understanding how far you need to be behind the car in front.

There are also a number of factors that you are responsible for. Making sure you stay on top of these will help to reduce your stopping distance:

  • Your car’s condition can increase its stopping distance.  Worn brake pads, poor quality tyres or tyres not meeting the national requirements can all send stopping times soaring. All of these things are checked during your MOT, so if you are due an MOT, book today to avoid facing these issues.
  • As a driver, you are responsible for remaining alert and vigilant at all times. Do not drive if you are under the influence of alcohol or drugs as they could cause an increased reaction time which could prove fatal. Things such as tiredness, heat and illness can also have an effect so only drive if you feel well enough to do so.

If you’re looking to decrease your stopping distance, speak to a member of our friendly team today! They may book you in to replace your brake pads or tyres in one of many locations across the country.