Understanding stopping distances in all weather conditions
When driving a vehicle in any type of weather, understanding stopping distances at different speeds is paramount
Whether it’s coming to a slow, controlled pause at traffic lights or an emergency stop to prevent a collision, it’s vital that you’re able to brake in time when you’re behind the wheel.
One of the biggest contributors to road traffic accidents is driving too closely to the rear of the car in front – otherwise known as tailgating. Highways England reported that more than 100 people are killed or seriously injured each year in accidents concerning tailgating, with every one out of eight casualties on the road on the strategic road network citing tailgating as a factor.
While on the road, it’s important to consider potential hazards ahead as it could prevent a serious injury. However, with technology constantly evolving, there are plenty of new AI safety innovations that can help keep drivers alert and prepared while on the road, regardless of what kind of conditions they encounter.
Whether you’re a seasoned driver or you’re new to the roads, it’s crucial to remember car stopping distances and the effects different circumstances can have on them. Remember, it’s not only weather conditions that can have an impact but also the vehicle type and driving style too.
If any of the information throughout this article does not fit with the performance of your vehicle, you can book a full maintenance check at a garage convenient to you, using ServicePoint.
Thinking distance vs braking distance
Stopping distances are calculated by adding your thinking distance (the time it takes you to process the fact that you need to brake) to your braking distance (the time it takes for your car to come to a halt after you put your foot on the brake pedal). The faster you are travelling, the greater your stopping distance will be.
According to the Highway Code, minimum thinking distances are as follows:
20mph – 6 metres
30mph – 9 metres
40mph – 12 metres
50mph – 15 metres
60mph – 18 metres
70mph – 21 metres
Thinking distance figures are based on a reaction time of 0.67 seconds, which assumes that drivers are alert and concentrating. However, according to research commissioned by road safety charity Brake, the average thinking time for drivers is in fact 1.5 seconds.
Your thinking distance shouldn’t generally be affected by weather, unless the conditions outside your car make it harder to spot and react to hazards. However, your braking distance (and therefore your overall stopping distance) will be heavily influenced by conditions on the roads.
The Highway Code states that average breaking distances in normal conditions are as follows:
20mph – 6 metres
30mph – 14 metres
40mph – 24 metres
50mph – 38 metres
60mph – 55 metres
70mph – 75 metres
However, anything that reduces friction between your car’s tyres and the road will have a negative effect on your ability to stop quickly. For example, it takes longer to brake on wet or icy roads than on dry surfaces because it is harder to get traction in these conditions.
How to calculate stopping distances
There is a good and quick way to calculate overall stopping distances. If you start at 20mph and then multiply by increasing intervals of 0.5 for every 10mph increase in speed, you will get the stopping distance in feet. This can easily be converted into metres by dividing by 3.3.
This would be as follows:
20mph x 2 = 40 feet (12 metres)
30mph x 2.5 = 75 feet (23 metres)
40mph x 3 = 120 feet (36 metres)
50mph x 3.5 = 175 feet (53 metres)
60mph x 4 = 240 feet (73 metres)
70mph x 4.5 = 315 feet (95 metres)
How to remember stopping distances
You’ve probably heard of the two-second rule, and it’s a good one to follow in dry conditions. This means choosing a fixed point on the road in front of you and registering when the vehicle ahead of you passes it. As long as two seconds or more elapse before you reach the same point, you’ll probably have enough time to stop in an emergency.
If the road is wet, you should double this gap to four seconds - and if it’s icy, try to leave a significantly larger gap.
How do weather conditions affect breaking distances?
Research suggests that braking distances can double in wet conditions, and could even increase tenfold in snow or ice. So, if you want to be able to stop safely when the weather takes a turn for the worse, you’ll need to reduce your speed and leave a bigger gap between your car and the vehicle in front of you. There are other dangers to be aware of too:
In heavy rain, you may find that your vehicle starts to aquaplane. This happens when your tyres fail to disperse standing water efficiently enough and a layer of liquid forms between the rubber and the road, causing you to lose control. Brakes are ineffective when you’re aquaplaning.
The initial reaction in this situation is to immediately apply the brake. However, you need to remain calm and consider the following:
- Firmly grip the steering wheel and calmly steer the vehicle in the direction you want to go
- Ease of the accelerator and gently pump the brakes
- Do not accelerate or brake quickly
Snow and Ice
When you’re travelling in wintry conditions, snow and ice can become compacted in your tyre tread, significantly reducing the effectiveness of your tyres and meaning they lose their grip. This is why braking distance on ice and snow increases monumentally.
If your vehicle begins to encounter problems while driving on snow and ice, consider the following:
- Don’t hit your brakes, as this could result in your vehicle becoming more unstable
- Turn your vehicle into the direction of the slide
- Stay calm and don’t over correct yourself
How to reduce braking distances
There are a variety of things you can do as a driver to reduce your braking distance. Here are some of the most important:
Ensure your tyre tread is up to scratch
By law, tyres must have a minimum tread depth of 1.6mm. Anything below this could result in you being fined and receiving penalty points on your licence. However, it’s advisable to change your tyres well before the tread wears down to this level. This is because as their tread reduces, your tyres’ ability to grip the road decreases.
Research has shown that at 30mph on a wet road, a car with tyres featuring 8mm of tread can come to a stop in 25.9 metres. Travelling in the same conditions at the same speed, a car with tyres with 3mm of tread will take 35 metres to come to a halt. When the tread is 1.6mm, the stopping distance increases to 43 metres.
Safety experts suggest that you shouldn’t let your tyre tread get below 3mm. If you think you need new tyres and would like to have your vehicle assessed on stopping distances, have a look at our range of services and book in for a consultation with one of our engineers today.
Choose good quality tyres
The tyres you choose can also have an impact on your braking distance. When travelling at 70mph in wet conditions, cars fitted with budget tyres may take an extra 14 metres to stop compared with cars that are fitted with premium tyres. This difference can be around five metres when travelling at the same speed in dry conditions. Premium tyres have other safety benefits too, including increased resistance to aquaplaning.
Keep an eye on tyre pressure
Your tyres must be inflated to the correct pressure at all times. This helps to maximise their contact with the road surface, allowing you to stop more quickly. Underinflated tyres will make more contact with the road on their outer edges, whereas overinflated tyres make more contact across the centre of the rubber. Both of these scenarios are bad when it comes to your braking distance.
It’s advisable to check your tyre pressure every couple of weeks or before long journeys. Make sure you do this when your tyres are ‘cold’, meaning your vehicle has been stationary for two hours or more.
Maintain your brakes
Keeping your brakes in good working order is essential. This includes replacing brake pads before they wear down too much. Also, if you’ve driven through deep water, it’s useful to pump your brakes a few times while travelling slowly. This will help to dry them out and ensure they’re functioning properly when you need them.
What other factors can affect stopping distances?
As well as finding ways to cut your braking distance, you should keep your thinking distance to a minimum. The following suggestions will help you to achieve this:
According to a study conducted by Loughborough University, one in six crashes that result in death or injury on major roads are fatigue-related. It’s well known that being tired can impair your ability to make decisions and slow your reaction time. So, don’t get behind the wheel if you’re feeling sleepy, and if you become tired while driving, find somewhere safe to stop and take a break
Try to plan long journeys to give yourself time to take a 15-minute break every two hours, and share driving duties where possible. Stay hydrated during journeys too.
Ensure good visibility
You can’t react to potential hazards on the road ahead if you can’t see them, so it’s vital that you have good visibility. Make sure your windscreen washer fluid levels are always topped up and your wiper blades are in good condition. Also, don’t be tempted to set off too quickly on frosty mornings. Clear your windscreen of any ice and condensation before you pull away.
It’s all too easy to get distracted behind the wheel, particularly now with all the gadgets and in-car tech available. Mobile phones are one of the biggest distractions, so avoid using yours when driving.
With any journey, stopping distances can vary according to a range of factors, including the weather, how well you maintain your car and how alert you are to what’s going on around you. The important thing is to know what to expect when you apply your brakes and to adjust your driving according to the conditions on the road.
As the weather changes, it’s important to make sure that your vehicle is prepared for winter conditions. With ServicePoint, drivers and fleet managers can benefit from fleet servicing, maintenance, repairs and MOTs to help keep your vehicles in top condition. Simiarly, our our Fuel Assist program from AA as well as their Pay-as-you-go Roadside Repair option helps you if one of your vehicles breaks down or you put the wrong fuel in the tank.
For more information on how Allstar can help you, call our team on 0345 266 5101. Alternatively, click the ‘Request a callback’ link at the top of the page and we’ll give you a call at a time that suits you.