Stopping Distances

Weather

The weather reduces a driver's ability to stop quickly for two main reasons. It reduces visibility, meaning drivers take longer to spot hazards, and the vehicle's tyres have less grip on wet road surfaces, which means it takes longer to stop, and in the worst cases, the driver may lose control of the vehicle and skid.

In very bad conditions, avoid driving completely, unless you absolutely have to make the journey and driving is the only option.

It's a good idea to have your vehicle fully serviced before winter starts.

It is very important to adapt your driving according to the weather and road conditions:

Drive at a safe speed for the conditions.
Whilst the speed limit sets the maximum speed for the road, in poor weather it can be dangerous to drive at the limit. Reduce your speed to give you more time to make observations, and reduce your braking distance.

Leave more space between yourself and the vehicle in front.
Braking distances are increased on wet roads, so you need to ensure you have plenty of space to brake into. Vehicles will also create spray in the wet and you need to ensure that this does not restrict your visibility.

Drive smoothly.
Avoid harsh braking and acceleration, or sharp steering.

Remember that other road users may not see you.
The reduced visibility may affect how other road users see your vehicle too, and you should not assume that they have spotted you. When you spot another vehicle, always try to plan what you would do if they manoeuvred or pulled out, because they had not seen you.

Give cyclists and motorcyclists plenty of room.
They may need to move out or manoeuvre to avoid large puddles or drain covers.

Regularly check the tread depth of your tyres.
This is something that you should do frequently, especially in the winter when you are more likely to get caught in the rain. Tyre tread helps to remove water from in between the tyre and the road surface, and the greater the tread depth, the greater the volume of water it can remove. The legal bare minimum tread depth is 1.6mm around the circumference of the tyre, but RoSPA recommend that tyres are changed once the tread depth is down to 3mm.

Use dipped headlights.
Rain reduces your ability to see and greatly increases the distance required to slow down and stop. Remember that you will need about TWICE your normal braking distance. Use windscreen wipers, washers and dipped headlights; drive smoothly and plan your moves in plenty of time.

The Simulator and Wet Weather

The simulator allows you to compare the stopping distances at different speeds, on wet or dry roads by ticking the wet weather box.

A car's overall stopping distance is made up of the driver's thinking distance (the distance the car travels from the point when the driver realises they need to brake and they actually start to brake) and their braking distance (the distance the car travels from the point when the driver starts to press the brake pedal and the vehicle comes to a complete stop).

During rainy conditions, and afterwards when there is water on the road, the car's tyres will have less grip on the road surface. The slippery road surface will increase your braking distance.

When the wet roads option is chosen in the simulator, the grip that the vehicle has with the road is reduced to show how the braking distance will increase in wet weather.

Reduced visibility can decrease visibility on the road as well, and it may also take longer to spot other road users, although this has not been factored into the thinking distance in the simulator.