February 2022

One of the questions on the driving theory test that often causes consternation is about stopping distances. If you were put on the spot today could you recall how many metres it takes an average car to stop at 30mph? How about the difference it makes in the wet?

The longer it has been since sitting your driving test the hazier this information might be, though the gut feel you get from real-world experience of driving at different speeds and on different roads goes some way to balance this out.

That said, perhaps it’s time for a brush up, so here’s a quick run down on what we should all be aware of.

What is a car's stopping distance?

Put simply, it’s the distance the car travels between the moment you first notice that there could be a reason to brake, and when it comes to a full stop.

Your overall stopping distance is made up of 3 elements:

  • Thinking distance - how long it takes you to see the situation and decide you need to brake
  • Reaction distance -how long it takes you to actually press the brake pedal once you’ve decided this is what you’re going to do
  • Braking distance -how long it takes for the car to come to a stop once the brakes have been applied

There are a number of factors that contribute to each of these.

Your state of mind and level of alertness can make a big difference to how long it takes you to process what you’re seeing and make the decision to brake, which is why it can be so dangerous to be distracted by phones or tiredness.

If you’re in an unfamiliar vehicle or wearing unsuitable shoes it can take longer to actually press the pedal, and of course there are many factors that can increase your braking distance.

The road conditions, the condition of your tyres, how well inflated they are, whether or not your ABS kicks in, how heavily laden your car is (including additional passengers), and the gradient of any slope you happen to be on.

How long does it take to stop?

One of the most important things to remember about stopping distance is that even a small increase in speed can result in a large increase in how long it takes to stop.

Although thinking and reaction distances will increase proportionally, the actual braking distance increases much more.

A critical example of this is for speeds between 30 and 40 mph. At 30 mph the stopping distance for an average vehicle is 23 m or 6 car lengths but at 40 mph it’s 24 m or 9 car lengths... thats 50% further!

The 2 second rule

It’s a good idea to refresh your memory of these stopping distances and how they increase with speed. The 2 Second Rule suggests that the gap between you and the car in front should be a minimum of 2 seconds, but this really is the bare minimum!

If you think in terms of car lengths, on a motorway doing 70 mph there should be 24 car lengths between you and in a 30 mph zone there should be 9.

This may help you visualise the distance you should be leaving better than just thinking in terms of metres or feet.

Weather conditions

We mentioned some of the factors that can affect braking distances earlier, but the weather conditions deserves a special mention.

On wet roads stopping distances can be doubled, and up to ten times when conditions are icy. This really is a sobering factoid and indicates how much more care and attention we need to be paying when it’s wet or cold.

Tyre condition

One of the major contributors to stopping distance is the condition of your tyres. If they are worn but still with a legal tread depth, they could negatively affect their ability to bring your car to a halt.

Take a look ad this blog on tyre safety and car, and make sure you are checking them regularly for wear as well as maintaining them at the correct pressure. 

Tyre Tips Blog

Can stopping distances affect my insurance premium?

Some insurers, especially those geared towards younger and more inexperienced drivers, can insist on a ‘black box’ recorder being installed in your car. This collects data about how safely you are driving, including your braking habits.

Although it’s not strictly the braking distance itself that will have an impact, when it comes time to renew this data may be used as evidence to increase (or decrease in the case of safe driving habits) your premiums.