Stopping Distances

You will more than likely come across a question or two about stopping distances or braking distances when taking your theory test – concepts which can be memorised and applied to real-life scenarios quite easily. This article will help you understand the terms used as well as help you make sense of them when taking your test.

When preparing for your theory test, you should be aware that there are several different types of distances, each one with a different name and meaning. These are:

  • Thinking distance
  • Reaction distance
  • Braking distance
  • Overall stopping distance

When answering a theory test question about stopping or braking distances, it’s crucial you read it carefully. For example, if you answer a question about braking distance, thinking you are answering a question about stopping distances, you’ll inevitably get the wrong answer.

Let’s look at these in further detail.

Thinking Distance

What is thinking distance?

Thinking distance is the distance you travel in the time that it takes you to realise there’s reason to stop. This time will include:

  • seeing the situation as it develops;
  • identifying that there’s a risk and;
  • deciding that the circumstances require you to brake in response to this risk.

You need to bear in mind though that the faster you’re driving, the longer such reactions will be here.

What factors affect the thinking distance?

  • Your state of mind – Are you are focused and alert, with your concentration solely on your driving session, ready for any possible hazards which may present themselves during your journey? Or, do you find that you’re immediately distracted before you even step into the car, therefore unable to switch off and dedicate the session to concentrating solely on your driving, or do you feel tired and lethargic beforehand?
  • Your driving experience and your ability to respond to hazards – Have you been taking your lessons for some time now and do you feel confident with being out on the road, finding your response time quickening with each journey? Or, do you struggle from a lack of confidence behind the wheel and find yourself missing vital clues about upcoming hazards?
  • The distractions present in your car – Do you find it difficult when people are in the vehicle with you and, more so, when they attempt to make conversation with you? Does listening to music or the temptation of using a phone immediately distract you?
  • Any possible impairment you may have – Have you been drinking before getting into your vehicle or are you under the influence of any drugs? Remember, this can also refer to those drugs that are prescribed to you as medication from your doctor as some can result in a feeling of drowsiness whereby driving a car is not recommended. Additionally, do you feel unwell and believe you will struggle to concentrate due to feeling ill as you operate your vehicle?

If you are an experienced driver who is fully alert to your surroundings, and not distracted nor impaired, your thinking distance should fall between half a second to one second. For inexperienced, distracted or impaired drivers, this will extend to two seconds, and a lot longer should the driver get distracted by a mobile phone.

Note: You may be wondering where the thinking distance is mentioned in the Highway Code? Though it might talk about thinking distance, in effect it doesn’t actually mean the same thing! Rather when referring to thinking distance, the Highway Code actually means “reaction distance”, which we will discuss next.

Reaction Distance

What is reaction distance?

This is the distance travelled by your vehicle in the time it takes for you to move your foot from the accelerator pedal and apply it to the brake pedal while pressing down hard in order to slow the vehicle down.

What factors affect the reaction distance?

  • Lack of driving experience
  • Tiredness
  • Driving in an unfamiliar vehicle
  • Driving while under the influence
  • Wearing the wrong shoes to drive in

During your practical test, you may be asked to perform an emergency stop manoeuvre. Your examiner will pre-warn you about carrying this out and will then slap the dashboard to indicate that you need to start braking immediately. The time you take to begin braking here will be your reaction time, with your reaction distance that of the time your examiner slaps the dashboard to the time you initially apply the brakes.

Once again, if you’re a fully experienced driver in a familiar car, your reaction distance should be around 0.7 seconds, with the less experienced or impaired driver in an unfamiliar vehicle looking at 1.5 seconds plus.

Note: The Highway Code charts label reaction distance as thinking distance here.

Braking Distance

What is braking distance?

Braking distance is the distance that you travel in your vehicle from when first applying your brakes to that point whereby your car stops completely.

What factors affect braking distance?

  • Your driving skill.
  • Whether the vehicle your driving has ABS or not.
  • The state and condition of your vehicle’s tyres – This can include issues such as their pressure, the wheel tracking and its accuracy, the quality of the rubber used in your tyres and other such things like tread depth and even tread pattern.
  • The state and condition of the road surface you’re driving on – Road surfaces can make a difference especially if they involve loose gravel, potholes or poorly tarmacked roads.
  • The weather conditions – From wet and icy to dry roads, each weather type brings its own challenges for drivers to contend with.
  • Whether you are on a slope – You will notice significant differences in your braking distance when going downhill, uphill or even when level.
  • The quality of your vehicle’s suspension – More importantly, how well your suspension is maintained.
  • The quality of your vehicle’s braking components – Crucial checks here need to be based around your brake pads, discs, shoes, and drums, ensuring they are also maintained on a regular basis.

The most important point to remember here is that doubling speed more than doubles braking distance. Even just a small increase in speed will cause a substantial increase in braking distance.

It usually comes as a surprise to many taking the theory test that the weight of a vehicle has no bearing on braking distance. The reason for this is simple; it is the friction between the tyre and road surface which controls the braking distance. The more a vehicle weighs, the more friction is present. Thus, the two cancel each other out.

Overall Stopping Distance

What is stopping distance?

This is the total distance travelled while you, think, react and brake. Everything mentioned above will, therefore, play a part in affecting your stopping distance.

Why is information about stopping distances important?

  • You can use this information to accurately judge the distance between your vehicle and the one in front of you
  • You can begin to understand how much of a gap you should ideally leave by how far it takes you to reduce your speed
  • You’re more likely to drive sensibly rather than tailgate the vehicle in front
  • You will learn how vital it is to extend your gap to account for poor driving conditions
  • Finally, you’ll be prepared for your theory test questions on the subject!

Note: The overall stopping distance is also regularly referred to simply as the stopping distance. Once again, though it is shown in the Highway Code, it does ignore the element of the thinking distance. It does, however, include reaction distance, but you will find this labelled as thinking distance.

Converting between metres and feet

Another thing you may notice during your theory test revision is how all distances are referred to in both metres and feet, with one metre approximately measuring three feet. As a quick and easy guide, always remember that one meter is roughly three feet; therefore, you can:

  • Divide metres by three to get feet
  • Multiply feet by three to get metres

Stopping distances chart

You will notice from the Highway Code that there is an official chart included which clearly labels and details typical stopping distances. It’s strongly recommended that you work on learning this chart, as it will help you with your theory test, should you be presented with a question about stopping distances.

Many people find that a visual aid such as this one is one of the most powerful ways of recalling detailed information, rather than having to memorise extended formulas. Yet, while this is a great method for some, a large number of people studying for their theory test will also want to access an easy to use calculation to refer back to.

Stopping distances formula

You may use the following formula to calculate stopping distances:

x2 ÷ 20 + x = overall stopping distance measured in feet

where x is the starting speed.

For example, if your starting speed is 30 mph, the stopping distance calculation is as follows:

302 ÷ 20 + 30 =
(30 × 30) ÷ 20 + 30 =
900 ÷ 20 + 30 = 75 feet

Further stopping distance examples:

20 mph: 20 + (20 × 2) ÷ 2 = 20 + 20 = 40 feet
30 mph: 30 + (30 × 3) ÷ 2 = 30 + 45 = 75 feet
40 mph: 40 + (40 × 4) ÷ 2 = 40 + 80 = 120 feet
50 mph: 50 + (50 × 5) ÷ 2 = 50 + 125 = 175 feet
60 mph: 60 + (60 × 6) ÷ 2 = 60 + 180 = 240 feet
70 mph: 70 + (70 × 7) ÷ 2 = 70 + 245 = 315 feet

Two-second rule

You may hear the two-second rule being banded around by many drivers who have years of experience behind them. On motorways in particular, a two-second gap is the absolute bare minimum that you should be leaving on such roads.

This is all about keeping a reasonable distance between yourself and the vehicle in front but isn’t always the most appropriate for those who struggle to visualise it in practice.

Instead, aim to look at possible car lengths as your approximation when considering your overall stopping distance in real-time. This is a more practical way to apply the required distances in metres or feet.

The best way to do this, and perhaps an easy visualisation trick to master, is to assume that an average car length will be around the four to five-metre mark, which is around 12 to 15 feet in length. Say you are travelling to the standard speed limit of 70mph on the motorway and, according to the Highway Code, your stopping distance overall here should be 315 feet as a guide. This effectively means you are looking at around the 105-metre mark for your stopping distance. To be able to visualise this better, this equates to around 21 to 25 car lengths.

Stopping distances in rain and ice

Finally, always remember that hazardous weather conditions will significantly affect stopping distances. Though they won’t affect your thinking and reaction distance, you will need to be aware that your overall stopping distance will greatly increase when braking.

If you must venture out in such conditions, remember to implement double the braking distance in wet conditions and as much as ten times the braking distance when it’s icy, at least. You will also need to remember here that when you attempt to slow down on an icy road or even when attempting a downhill road in treacherous conditions, the grip of your tyres will at this stage be unable to overcome gravity and instead likely accelerate. More so, it won’t really make a difference here as to what moves you make with your steering or your braking, which can be a scary moment for even the more experienced drivers.

Many driving experts will advise all drivers, regardless of how many years they have been driving to avoid such conditions as much as they possibly can. However, if that isn’t at all possible, then caution needs to be taken alongside a thorough and adequately prepared vehicle for the journey which you can adapt to suit current conditions.

Developing good habits

Get into the habit early on of practising implementing a decent-sized gap between you and the vehicle in front of you at all times, along with building up your knowledge of how to calculate average stopping distances in all-weather types. This will then certainly stand you in better stead and allow you to continually act on such information as and when you need to when driving in your vehicle.

After passing your theory and practical tests

Once you have successfully passed your theory and driving tests, you may want to look at driving out further afield and get a taste of driving on the motorways. When driving on motorways, it is vital that you leave a large gap in front of you to ensure you allow enough time to stop or reduce your speed quickly, should the vehicle in front of you slow down or stop without much warning.

Unfortunately, you may come across other such drivers who have no care or consideration for stopping and braking distances, meaning several cars may well fill in such a gap during your journey – but stick to what you have been taught.