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How Do Weather Conditions Affect Stopping Distance?


Modern car parked outdoors on rainy day

It is a known fact that the weather in the UK is extremely unpredictable. From rain to slush, to snow and fog, the weather reduces a driver’s ability to stop quickly and safely, which can cause one of two things (or even both).

Adverse weather conditions reduce visibility, which means it’d take drivers longer to spot a hazard, and the vehicle’s tyres are prone to have less grip on wet to wintry road surfaces, meaning it would take longer for a vehicle to stop, to which the driver may lose control of the vehicle and skid.  

When driving a vehicle, regardless of the type of weather, it’s crucial that you understand stopping distances at different speeds. The reason that this is paramount is to ensure your safety as well as the safety of other road users.

It’s crucial that you’re able to adapt your driving in line with the weather and road conditions. But before you do this, make sure that your vehicle is fully serviced before winter begins.

Average braking distances

According to the Highway Code, the average breaking distances in normal conditions are as follows:

Speed                 Braking Distance                                  
20mph6 metres
30mph14 metres
40mph24 metres
50mph38 metres
60mph55 metres
70mph75 metres

The two-second rule is great to follow in dry conditions, however, if the road is wet, be sure to double this gap to four seconds, and if it’s icy, ensure you leave a larger gap between your car and the vehicle in front of you. This will allow you to brake in the safest way.

It’s worth noting that the average stopping distance can be calculated like so: 

Stopping distance = thinking distance + braking distance. 

So whether you’re a seasoned driver or new to the roads, it’s important to remember that car stopping distances will be affected by different braking distances, so ensure your driving style is both safe and convenient for the vehicles around you.

Rain

When in heavy rain, you may find that your vehicle will begin to aquaplane, if this happens then firmly grip the steering wheel and ease off of the accelerator whilst gently pumping the brakes. The reason cars aquaplane is due to the tyres failing to disperse standing water, which then forms liquid between the rubber of the tyre and the road. This would then cause your brakes to become ineffective.

Snow/Ice

The grip of your tyres can be compacted in the tyre tread, which may reduce the effectiveness of your tyres and this will then mean they’ll lose their grip. To prevent this from happening, be sure to stay off the brakes as this may result in the car slipping and sliding. If for some reason the car does begin to slide, turn the vehicle in the direction of the slide and stay calm whilst doing so.

As your stopping distance could increase tenfold during rain or snow, here are some tips for when driving in bad weather conditions, which will reduce braking distance:

Driving at a safe speed

Despite the speed limit being set by the maximum speed for the road, in adverse weather condition, it may be dangerous to drive at the limit. Ensure you reduce your speed, this will give you extra time to observe your surroundings to then reduce your braking distance.

Leave space for vehicles in front

Braking distances are increased on wet roads, so it’s important that you ensure you have plenty of space in front of you to brake into. During wet conditions, it’s important to note that the vehicles in front create a spray, thus, you need to ensure that this does not restrict your visibility.

Give cyclist and motorists room

Allowing cyclists and motorists space is of vital importance. A good rule of thumb is that the distance should be around 1.5 metres, which is also dependent on speed. It’s crucial that you take extra care and give plenty of space when overtaking as cyclists may move towards the middle of the lane to avoid potholes and so on.

Use dipped headlights

Rain, fog and snow reduce your ability to see, which significantly increases the distance that is required to slow down and stop. Remember that you will need almost twice your normal braking distance when it is raining.

Be sure to utilise your windscreen wipers and drive carefully and plan your driving in plenty of time. Likewise, to ensure you avoid dazzling other road users during wintry conditions, remember to dip your headlights.

Check your tread depth often

Regularly checking your tread depth will prevent you from getting caught in the rain or snow. Having correct tyre tread helps to remove water from in between tyres and the road surface. Thus, the better the tread depth is, the larger the volume of water it can remove.

Remember that the minimum legal tread depth is 1.6mm around the entire circumference of the tyre. Try taking the 20p test if you’re unsure if your tread depth is at the legal limit. Alternatively, you can try using a tyre tread depth gauge to establish what your tread depth is at.

  • How Do Weather Conditions Affect Stopping Distance?
  • How Do Weather Conditions Affect Stopping Distance?

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