31 May

Stopping distances: everything you need to know

Andy Moody
Car Guides

Whether you are a learner driver studying for your theory test or want to refresh your skills, it is essential that you understand the Highway Code and how to calculate stopping distances.

Our guide will cover everything you need to know about stopping distance rules. It is essential to understand the distance you need to maintain between you and another vehicle and answer any questions you may have.

What Is Stopping Distance?  

The overall stopping distance is how far a moving car has travelled to bring it to a standstill.

The stopping distance includes:

  • The thinking distance – is how long it takes before you react.
  • The braking distance – the time it takes for the car’s brakes to bring the car to a stop.

Why Is It Important To Know Stopping Distances? 

By understanding stopping and braking distances, you will be able to judge the space needed between the car ahead of you and your car. This means you will have plenty of reaction time if someone suddenly stops and have full view of the road ahead, avoiding a collision.

To protect yourself in case of an accident, it is good to protect you, our learner driver insurance or temporary insurance can make sure you are covered.

What Is The Stopping Distance Formula? 

The Highway Code has a formula for stopping distance:

Stopping distance = braking distance + thinking distance

This formula can be used at different speeds to determine how long it will take your car to come to a complete stop.

How Much Stopping Distance Should You Leave?

Certain factors will influence the stopping distance, like the road surface condition, the condition of your brake pads, how fast you are driving, and how quickly you can react.

The Highway Code formula uses the average car length for UK cars and assumes the road is dry when calculating stopping distances.

Stopping Distances At Different Speeds

If you take your theory test, you will have to remember average stopping distances at different speeds. Let’s take a look below at these:

Stopping distance at 20mph  

At 20 mph, the stopping distance is 12 metres (40 feet) and is calculated by:

  • 6m braking distance + 6m thinking distance = 12 metres

Stopping distance at 30mph  

At 30mph, the stopping distance is 23 metres (75 feet) and is calculated by:

  • 14m braking distance + 9m thinking distance = 23 metres

Stopping distance at 40mph  

At 40mph, the stopping distance is 36 metres (118 feet) and is calculated by:

  • 24m braking distance + 12m thinking distance = 36 metres

Stopping distance at 50mph  

At 50mph, the stopping distance is 53 metres (175 feet) and is calculated by:

  • 38m braking distance + 15m thinking distance = 53 metres

Stopping distance at 60mph  

At 60mph, the stopping distance is 73 metres (240 feet) and is calculated by:

  • 55m braking distance + 18m thinking distance = 73 metres

Stopping distance at 70mph  

At 70mph, the stopping distance is 96 metres (315 feet) and is calculated by:

  • 75m braking distance + 21m thinking distance = 96 metres

How To Calculate Stopping Distance 

It could be very underwhelming to remember the braking and thinking distances to calculate the stopping distances at each speed.

Luckily, there is an easy trick to help you remember:

If you calculate the stopping distance in feet, multiply your speed by intervals of 0.5, and start at 2 for 20mph.

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

To get from feet to metres, divide by 3.3. (e.g. 40 feet/3.3 = 12m). You might need a calculator for this. However, it is unlikely you will require it for your exam.

What Is Thinking Distance?

The distance a car moves while a driver thinks about stopping is known as the thinking distance.

If there is a hazard, the driver will realise they must stop and then step on the brake pedal. On average, this takes about 0.7 seconds, but the distance the car travels in that time will depend on the car’s speed.

What Factors Can Affect Thinking Distance?

The thinking distance will be influenced by the following factors:

Drugs and alcohol

When drinking or taking drugs, your reaction time will be slower. A slower reaction means the car will travel further before stepping on the brakes.

Distractions

Any distraction that takes your attention away from the road will increase your thinking distance. Examples of distractions are:

  • Conversations with passengers
  • Changing the radio or air-conditioning settings
  • GPS devices and mobile phones

Tiredness

A tired or sleep-deprived driver will have a slower reaction time because they are less alert. To avoid this, drivers should take a break after 2 hours of driving.

Visibility

If it is raining or misty, drivers will have less visibility, which will increase the thinking distance.

What Is The Braking Distance?

The braking distance is how long it takes the car to stop once the driver applies the brakes. A car travelling at greater speeds will cover more distance before coming to a complete standstill and therefore have a bigger braking distance.

What Factors Can Affect Braking Distance?

Below are some factors that will influence the braking distance:

Weather conditions

Wet or ice on the roads will require an increase in the braking distance. This means you should double the gap between you and the car ahead of you if the road is wet and even more so if there is ice on the road (some suggest increasing the gap ten times), so make sure your car is ready for winter.

The condition of the vehicle’s tyres

Tyre conditions will influence the level of grip it has on the road. Tyres also have different dry and wet grip, depending on the type of tyre. Braking distances are also affected by the pressure of the tyre. Both over and under-inflation will increase the distance the car travels to come to a stop.

Road conditions

Roads in poor condition with potholes and uneven surfaces will increase the braking distance. Muddy or wet roads will also result in a longer braking distance. If the road is icy, the length it takes the car to stop can be ten times longer. 

The weight of the vehicle

A heavier car will have a longer braking distance.

What Is The 2-Second Rule?

The 2-second rule is a quick rule of thumb to ensure enough distance between you and the car in front.

How does the 2-second rule work?

Here is how the two-second rule works:

  • While driving, find a fixed point coming up on the road
  • Take note of when the car ahead of you goes past your selected point
  • Count two seconds (or more), and then pass the same point
  • If it took you two seconds or longer to pass the fixed point, there is a safe distance between you and the car ahead

The 2-second rule applies to dry conditions. If the road is wet, increase the time to 4 seconds.

Should Stopping Distances Be Updated?

The above stopping distances have been used for decades. Over that time, cars and brakes have evolved and are much more advanced.

Many people think it is time to decrease the stopping distances, as cars can come to a stop much faster than before. Others say the distances should be increased as drivers have many more distractions with infotainment systems in their cars.

Also, making sure you and your friends are safe when your driving is essential. Discover our guide on how to plan a road trip with friends.

FAQs

What should your stopping distance be at night?

At night your stopping distance should be longer than during the day. A good rule of thumb is that your stopping distance should be within the distance your headlights shine up ahead.

Some people recommend that your stopping distance at night (if the road is dry and weather conditions are normal) should be the distance you travel in four seconds, using the four-second rule.

Check out our essential guide on how to be a safer driver at night.

 

Is there an easy way to remember stopping distances?

A trick you can use to calculate stopping distances in feet is to use the travelling speed and multiply it with intervals of 0.5, starting with 2 for 20mph.

For example:

  • 20mph x 2 = 40 feet
  • 30mph x 2.5 = 75 feet, etc.

This will help you remember the stopping distances for your theory test.

What’s the difference between stopping distance and braking distance?

Braking distance is used to calculate the stopping distance and is the distance the car travels from when you step on the brake pedal until when the car comes to a stop.

Stopping distance is calculated by using the braking distance plus the thinking distance and is the total distance the car travels from when you realise you have to stop to stepping on the brakes to coming to a complete stop.

What is the minimum stopping distance on a wet road?

It is recommended that the minimum stopping distance on a wet road is double that of the stopping distance on a dry road.

Improve your driving in the rain by browsing our wet weather safety tips.

Final Thoughts

Whether you are learning to drive or want to refresh your memory, it is good to understand the stopping distances required by the Highway Code. Knowing how many car lengths to leave between you and the car ahead will reduce your risk of being in an accident if you suddenly have to stop. However, if so, learn more about what to do after a car accident.