APPROXIMATE STOPPING DISTANCES

As can be seen by all the following comments, this is a very complex subject to which there is no definitive answer.  The figures shown are a very, very rough calculation which tie in with those featured in the current UK Highway Code.

UPDATE (August 2019)  -  this information does seem to change on a regular basis so, for the latest official data from UK authorities check out the government site at -

https://www.gov.uk/guidance/the-highway-code/general-rules-techniques-and-advice-for-all-drivers-and-riders-103-to-158#rule126

Weather/road conditions, type and condition of vehicle, load etc., not to mention the age, health and mental ability of the driver can all affect the time taken to react and stop.

If nothing else, these do highlight the amount of time and distance required to bring a moving vehicle to a standstill. The first comments, sent in by John Whittle, really do emphasis this point.

Regarding driving speeds and converting miles per hour into feet per second. 

Take the speeds figure; for example 30 mph. Halve this speed to give you 15.

Add the two figures together and this is approximately how far you will travel in one second at 30 mph i.e. 45 feet. 

At 70 mph we do the same. 70 plus half of 70 which is 35, add the two figures together means that at 70 mph we will travel 105 feet in one second. 

Makes you realise the reality and relationship of speed, time and distance, and why so many people end up in a pile up.

An even easier way to convert speeds into feet per second has been sent in by Ken Jarrett.

Halve your speed and you have the answer in yards/sec. almost exactly. To convert this into feet per second just multiply by 3.

Example 1:

60 mph  (halve speed = 30 mph) = 30 yards per second:  

multiply by 3 = 90 feet per second.

Example 2:

70 mph (halve speed = 35 mph) = 35 yards per second:

multiply by 3 = 105 feet per second.

 

The charts are featured at the foot of this page but the comments, hints and tips prior to that make very interesting reading!

I just want to point something out that seems to cause a lot of confusion for many drivers - the difference between THINKING time and REACTION time, and you might want to add this to your page.

This bit of information from John Ruller is informative but a bit confusing:

Let's try to clear this up. The 1.5 second figure that John mentions is in fact a combination of both THINKING time and REACTION time.

If we look at the Highway Code, what we see labelled as "thinking distance" isn't really thinking time; for example:

SPEED = 60mph

"THINKING" DISTANCE = 60ft

BRAKING DISTANCE = 180ft

OVERALL STOPPING DISTANCE = 240ft

IF the driver is aware of the hazard ahead and knows exactly what to do and when to do it, then The "thinking distance" that the Highway Code talks about is actually the time taken to transfer your foot (or on a motorcycle fingers and foot) to the brakes and begin to apply them. So in reality it's not "thinking distance", it's REACTION distance - and it's this reaction time that is commonly measured as being approximately 0.7 second.

However, to react promptly, the driver has to be already aware of the hazard and ready to brake, just like when doing the emergency stop for the examiner on test! You have to be thinking "I'm going to need to brake" and just be waiting for the correct moment - in the case of the driving test, your cue is the examiner banging his clipboard on the dash!

However, in real driving, the driver needs to SEE the developing situation, IDENTIFY the fact there is a threat and then DECIDE if the required RESPONSE is to brake.

This is the true "Thinking" distance and it has to be added onto the reaction time and stopping distance to get the true (and longer!) overall stopping distance that John mentions.

If the driver isn't aware of the hazard, either through lack of concentration and tiredness, because they are being distracted by something like a chattering passenger, radio, sat nav or mobile phone, or perhaps because the driver is inexperienced and hasn't been in that situation before, observations have shown this thinking time can be up to two seconds!

Kevin Balding - I notice that you have a number of ways of working out stopping distances and all of them involve remembering numbers which frankly I'm not very good at so here is a formula which will do it for you (Only one thing to remember and I can do the maths in my head)

When trying to visualise a distance it is useful to remember that the length of an average car is approximately 15ft, therefore, 75ft would be about 5 car lengths away.

Another way of judging distances has been sent in by Frederick Petersen - this uses a time factor.

David Redfern has kindly sent in the following comments including suggestions on visualisation methods for calculating the distance required which is probably a lot easier to remember when driving after passing your driving test.

I read your article on stopping distances and the laudable contributions by many experts, one or two I recognise having been in the driver training industry for a number of years.

The calculations and debate are great, very informative however I refer to your DOS to Windows conversion and the principles of this web site, make it all understandable for novices.

I have yet to meet anyone who has remembered the stopping distances they so studiously memorised when passing their test far less the Speed = Distance/Time calculation a week after passing their driving test.

The fact is, it's meaningless, just figures and as most of us learn by visualisation and experience it's no wonder we forget it.

I'll also dispel one myth here, the 'two second rule is nonsense', although I haven't worked it out, evidently its incorrect for all but one stopping distance in the Highway Code but what's more important is that if drivers are continually spotting stationary objects to check their distance from the car in front, how much concentration are they devoting to actually driving?

A cars stopping distance is the lowest common safety denominator. Ask any 'advanced' (I hate that elitist term) driver what the most important safety skill drivers should develop and they will almost all say "observations" (every single one I have asked) then ask them what it is in thick fog when observations are virtually useless and they will almost always say "stopping distance", the last and default safety position.

Unfortunately we confuse our learners by continually throwing figures at the problem when, by our own admission, there is still debate amongst the experts as to what should be considered the finite calculation.

The vast majority of cars on the road are driven by reasonably healthy adults with good eyesight and reasonable reactions. The highway code advises us to beware of other vulnerable road users so elderly drivers, people on their mobile phones, with kids in the car etc. should all be given more time and space by us.

For the rest of us, the visualisation of, say, 23 metres ought to be automatic, many guys will respond to "roughly a quarter of the length of a football/rugby pitch" (and yes I know they vary in length but it's better than nothing). From that default the calculation becomes more manageable and I was taught that we should be looking at roughly 1 Yard for every mile per hour travelled. Times have changed and the Yard is now a metre, even more useful as at roughly 39 inches it's about 7%(?) more which gives us a nice little advantage but although it becomes less accurate above 50mph or so its memorable and more important, recognisable especially when drivers can visualise 23M then mentally multiply up.

One of you're contributors mentioned the problem of people overtaking and pulling into the gap they had left. I would remind him/her that the distance you leave between yourself and the car in front is also the space you need to leave for overtaking vehicles. The reality is, no matter what gap you leave, if someone is going to overtake you they will do it regardless of the gap in front of you, few people think that far ahead!