Highway Code stopping distance needs urgent review, experts say

stopping distance

New research has revealed that the stopping distance prescribed by the government’s Highway Code is too short. They now believe it could take drivers half as much time again to come to a halt in an emergency. Road safety campaigners have called on the government to undertake an urgent review. They want the stopping distance section of the Highway Code revised.

How is stopping distance calculated?

Experts split the length of time it takes a car to come to a halt into two. These are thinking time and braking distance. Thinking time is what it takes us to identify a hazard then for that message to travel from our brain to our foot and our foot to move onto the brake pedal. The braking distance is the amount of time it takes for the car to come to a halt once we’ve slammed on the brakes. Currently the Highway Code says it should take 12 metres to come to a halt from 20mph, 23m from 30mph and 96m from 70mph.

What should stopping distances really be?

Boffins from transport consultancy TRL examined a wealth of academic data that looks into drivers’ thinking time. They concluded that it takes much longer than the Highway Code estimates for drivers to see, recognise and react to an emergency. While the official thinking time is 0.67 seconds, TRL concluded that the human brain actually takes around 1.5 seconds. This is the figure used by the US equivalent to the Highway Code. And in Canada it’s 2.5 seconds.

Jason Wakeford from road safety charity Brake, which commissioned, the research explained: “We’re calling on the government to increase the stopping distances in the Highway Code as a matter of urgency. Even though car braking technology has improved in recent years, the majority of the overall stopping distance at most speeds is actually made up of the time taken to perceive the hazard and react. Our research shows that average thinking time is more than double that set out in the Highway Code.”

What does this mean?

According to the TRL’s calculations, rather than 12m, it will take 19m for a car to come to a halt from 20mph. That’s more than one and a half lengths of the average car more than the Highway Code. At 30mph, thinking time goes from 9m to 20m. That increases total stopping distance to 34m – nearly three car lengths more than the official figure. And at 70mph, thinking time goes up to 121m. This puts total stopping distance at just more than six car lengths longer than the Highway Code.

Speed 20mph 30mph 40mph 50mph 60mph 70mph
Revised stopping distances 19m 34m 51m 71m 95m 121m

Why Highway Code stopping distances are important

stopping distance

Get your stopping distance wrong and this is what happens

The Highway Code stopping distances are used by learner drivers as a gauge to judge their braking by. If that gauge is faulty and they think they can come to a stop quicker than they really can, they have a greater risk of crashing. Brake’s Jason Wakeford said: “A true understanding of how long it takes to stop a car in an emergency is one of the most important lessons for new drivers. Understanding true average thinking time reminds all drivers how far their car will travel before they begin to brake − as well as highlighting how any distraction in the car which extends this time, like using a mobile phone, could prove fatal.”

24 comments on “Highway Code stopping distance needs urgent review, experts say

  1. Eric Hayman 06/10/2017 8:53 AM

    There have been driving simulators around for decades. These can easily be used to see how long it takes for a person to react to, say, someone suddenly walking into the road, or another vehicle driving into the path of the simulator user’s route. Why has this not been done to establish reaction times? And why the vast differences between different countries? Are Canadians really slower thinkers?

  2. chris owen 06/10/2017 9:11 AM

    I have always treated braking distance as a matter of personal judgement. The figures don’t make any allowance for road conditions, eg rain. I explained this to my driving test examiner and he agreed with me.

    • Eric Hayman 07/12/2017 10:09 PM

      “I have always treated braking distance as a matter of personal judgement. The figures don’t make any allowance for road conditions, eg rain.” The same could be said about speed limits. Just as no speed limit can be said to be right for a section of road under all conditions (weather, traffic, etc), so it can be said that the Highway Code distances cannot be always right. But hey do give a framework for learners to use. Just as it only after taking a course of lessons and passing the driving test that a learner really starts to learn how to drive; experience is the biggest teacher. And it is experience that really teaches correct braking distances.

  3. Robert McLoughlin 07/10/2017 9:53 AM

    So much for current advances in tyre technology; one cannot account for stupid motorists who tailgate, drive too fast in adverse weather, traffic and roads.

  4. raymond stevens 16/10/2017 3:54 PM

    try taking into account the idiot overtaking you at say 50/60/70/80 mph plus suddenly cuts your front wing off, well almost then drops his speed slightly lower than your speed which was probably the limit, staying probably 20 foot in front of you.. Class act that one seen it to often

  5. daveoftruro 06/12/2017 9:28 AM

    I’ve had my reaction time tested on simulators and it’s far less than highway code times. The problem is that on the simulator you’re poised, waiting for the event to make you brake. Try driving for five hours,seeing the brake lights on the car in front and then realising it’s an emergency stop. I don’t think you’d approach 1.5 secs.

    • Rix Lumb 20/03/2019 9:07 PM

      I never focus on the car in front entirely, more like the cars in front of him, so my foot is over/on the brake before the car in front has touched his…

  6. paul watson 06/12/2017 4:47 PM

    stopping distances were for drum brakes,some new cars still have these on the rear,so
    there has not been a lot of interest in standards of design by the car industry,like every
    thing else it’s all about the bottom line and not a lot about safety.

  7. Robert Henry 07/12/2017 12:07 PM

    Good comment from Robert re tailgating and idiotic speeders!

  8. Steve Michelle 07/12/2017 12:14 PM

    This info update may possibly help learners to understand stopping distances, in order to get the written part of the test passed. But, it has no conection to reality. Under real conditions, stopping distance vary considerably, depending on driver, road condition, type of car, and possible distraction. Best solution, look where you are going at all times, don’t drink and drive, don’t take drugs, switch off mobile phones, and never reset sat nav on the move.

  9. Martin Leaver 07/12/2017 12:21 PM

    The Highway Code does say that distances should be doubled on wet roads.

  10. Stanley McWhirter 07/12/2017 5:51 PM

    Drivers think that as speed increases stopping distance increases; actually stopping distance increasingly increases, i.e. an exponential amount. As a driving instructor a favourite question to my pupils was – at 20 mph it takes 40 feet so at 40 mph how far to stop? The usual answer was 80 feet whereas it is actually 120 feet.
    Spotting a hazard early and easing off the gas early may not slow the car all that much but it reduces the stopping distance disproportionately.

  11. chris 11/12/2017 3:39 PM

    doubling speed increases kinetic energy 4 fold (speed squared) so assuming same maximum energy dissipation of brakes (converting K.E to heat) stopping distance from 40 mph is approx 4 times that of 20 mph ie 160 feet

  12. David Wrigley 12/12/2017 9:01 PM

    It is lack of attention that gives 1.5 seconds thinking time, instinct takes over in an emergency and there is ample research to prove that. If you have to think it out you have had insufficient training. (read the book “Thinking, Fast and Slow” by Prof. Daniel Kahnman,)

    Perhaps this is yet another devious scheme for extracting money from motorists. Are the police going to use these new figures to accuse motorists of dangerous driving. That must represent at least another 100 ft between the chevrons!! Where is this research paper? Where is the evidence? I simply don’t trust these government so-called research activities.

    My tested reaction time is around 0.3 second and I think that someone who has a reaction time of 1.5 seconds should seriously think of putting in some serious training for advanced driving, where they might learn some benefits of observation and assessment.

  13. Richard Smith 13/12/2017 11:27 AM

    Distances on roads are imperial, not metric. 95m – meaningless
    I took a driver awareness course several years ago and was told that the current stopping distances in the Highway Code were based on trials carried out in the early 60’s!!!!!!
    By the way, drivers who drive too slowly are also dangerous: 50mph in the middle lane is driving without due care but happens all too frequently. Probably driving at that speed so they can keep their halos in place.

  14. Bob dore 14/12/2017 6:22 PM

    I do not know, or wish to know the published stopping distances because I cannot accurately judge those distances. If the true stopping distance for given speed and conditions is 20m and my estimate of 20m is, in fact, 18m I am likely to cause an accident. If, on the other hand, I correctly know that I can stop before the car in front, whatever that distance may be, I will not cause an accident. Therefore I do not approve of theoretical stopping distances.

  15. Richard Wright 18/12/2017 10:26 AM

    To be realistic, stopping distances are a set of figures learnt for the test and then forgotten. The reason for this is that few people can sit in a car and estimate a distance ahead, even with practice. Also, judging a distance in terms of feet or metres adds another carriage to the train of thought and adds to the ‘thinking time’.

    Eventually judgement takes over; judgement can be good or bad.

    The best measure judging how far your car needs to be from the car you’re following is the time interval. As a learner or new driver, we should be instructing the 2 seconds’ gap on dry roads. For those interested in defensive driving that becomes habit and saves lives.

    For offensive drivers – those who have little sense of self-preservation behind the wheel – no amount of stopping distance adjustment or time interval will have any effect. Alas.

  16. Ian Treymayne 19/12/2017 12:13 PM

    Where on earth do these people get their figures from or are they just made up as they are not realistic distances. Anyone needing these distances to stop on dry roads shouldn’t even be driving but i suppose thats the nanny state for you

  17. Tony Jerrett 14/09/2018 2:56 PM

    It seems reading the report that the only research carried out was to find out what other countries used for their thinking time, nothing appears to have been done by TRL to obtain their own figures. As has been said in some of the posts above, the main thing in reducing stopping distances is concentration and seeing situations on the road developing before they happen. It is applying “what if to everything that is happening around you. As I was told many years ago by my driving instructor, who was an ex Hendon Police driving instructor, “If you need to make an emergency stop then you have failed in your observation”.

  18. Martin Leaver 21/03/2019 11:42 AM

    It’s not Reaction Time, it’s Thinking Distance; How long it takes to see the hazard, and then decide what to do about it. Slamming on the brakes may not always be the best action.

  19. P. Kiggell 06/02/2021 4:57 PM

    As a basic but general guide , I assume an average braking / stopping distance ( in metres ) of double my mph speed for both dry and wet conditions.

  20. Bill Owen 29/05/2021 1:56 PM

    So, thinking time is incorrect, that may be true, but. Obviously since the stopping distances in the Highway code were introduced (quite a while ago) there has been absolutely no improvement in tyre technology, suspension technology and also no improvement in vehicle braking systems whatsoever? Yet again we are seeing the “let’s not let facts get in the way of imposing needless restrictions on people” crowd come to the fore. I am not against increasing the stopping distances per se, but lets do it with all the facts and research taken into account.

  21. callum 12/07/2022 2:46 PM

    Even if thinking time is incorrect and i am not convinced i’m that slow, (!) the actual braking distances are so old that they are now 1/3 to 1/2 over estimated when compared to modern vehicles. The result of factoring this information in is a reduction in the quoted total stopping distance even when these huge thinking times are added in. Brake just want everyone to be on bicycles and so will obviously bash motoring at any opportunity until it becomes so inconvenient we will all be stuck in our homes.

  22. David 20/05/2024 4:53 PM

    Lots of factors are at play. We need to be careful what is communicated to new drivers and not provide them with inappropriate data out of good intent. Fortunately reaction times amongst the young are very good and diminish with age and fatigue. Factors that have changed since the stopping distances were determined need to be addressed. The use of improved pavement material both in terms of high PSV aggregates within more technologically developed binders has played a big difference in improving grip and improving road safety. Similarly improvements in tire technology has allowed cars to capitalize on improved surfaces.
    Cars themselves have changed dramatically since 1968. Advances such ABS, suspension and anti-role together with a reduction in unslung weight have improved control immensely. Hard breaking in a curve at speed would have been an unthinkably dangerous prospect for an untrained driver in 1968. It is pointed out that the safety improvements to cars has come at the expense of weight which although this has largely offset by material technology the most popular car of 1968 Morris 1300, 1040 kg was 240kg lighter than the most popular in 2024, Ford Puma 1280kg. I find it difficult to believe that a weight difference comparable to a tank of fuel and 2 passengers so impairs the breaking performance of the Puma to the point it is comparable with the Morris particularly given the improved road contact afforded by the additional weight.
    We need to stop lying to new drivers and tell them that modern cars can stop very quickly. Armed with this information they can leave appropriate distances between vehicles and avoid collisions.
    We need to publish real technical data and apply the reaction times of an Obese 65yo with Parkinson’s.

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