Guide to Stopping Distances

A stopping distance can be split into two parts – thinking distance and braking distance. Thinking distance is the distance needed for a driver to react to a hazard and step on the brakes. Braking distance is the distance travelled by the car while the brakes are slowing it to a stop.

If you’re in an average-sized family car travelling in normal weather conditions, the Highway Code gives the following guide to thinking distances at various speeds:

The Highway Code’s specified braking distances for those same speeds are as follows:

You might notice that at 20 mph, the thinking distance and the braking distance are the same – braking distance makes up half of the total stopping distance. At 70 mph, however, braking takes a lot longer, accounting for nearly 80% of the total stopping distance.

Adding together the thinking distances and braking distances listed above gives us the following stopping distances:

Do you think in imperial measurements? If so, you’ll have found the figures in brackets above useful, and you can also use this handy trick to help you remember stopping distances. Multiply your speed in mph by intervals of 0.5, starting at 20 mph x 2. This will give you your stopping distance in feet:

If you’re a fully metric person, you’ll need to divide those figures by 3.3 to get the distances in metres. Unless you’re a mathematical whiz, that will be a tricky sum to compute while keeping your eyes on the road, but dividing by three will give you a conservative set of stopping distances. Memorising the numbers given in metres above will probably be the easiest way to go about it.

As we mentioned at the top of the article, the car stopping distances given in the Highway Code assume an average-sized family car travelling in normal weather conditions. However, there are a number of variables that can affect the stopping distance needed.

As you might expect, bad weather conditions can mean a car and a driver will need longer to come to a stop. Bad visibility will increase the thinking distance, and a slippery road surface will mean it takes longer to brake. It has been suggested that wet conditions can double braking distances, while snow and ice can multiply them by a factor of 10. If you’re doing 20 mph in the snow, you might need to give the car in front the more space than you would if you were cruising on the motorway on a fine day.

It’s not only rain and snow that can make a road slippery. Gravel, oil spills and black ice can all make roads treacherous and mean you need a lot longer to brake.

It has been argued that modern cars, with their ABS systems and improved tyres, can stop much quicker than their forebears, and that therefore the Highway Code’s stopping distances should be updated. There are vehicles of all ages on the roads though, and there haven’t been any major upgrades to the human brain recently, so an automatic emergency braking system is the only innovation that will reduce thinking distances. Cheap or under-inflated tyres, or ageing brake pads, could mean you need longer to stop than the Highway Code stipulates.

The thinking distance component is entirely dependent on the person behind the wheel, and there are all kinds of factors that can slow down reaction times. Fatigue and age can come into play, as can distractions inside the cabin. Mobile phones, in particular, can have a huge impact on stopping times, especially if a driver checks theirs while travelling at high speed.

Understanding stopping distances is a crucial part of keeping yourself and others safe on the roads. Know how long it will take you to react and how long your car needs to slow down and stop, and distance yourself from the vehicle in front accordingly.

Read our handy guide to understand how your car brakes work and what you need to stay on top of to keep them in tip-top condition.