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Braking distances - Engineer Andy

I see that the 'charity' (IMO read anti-motoring pressure group) Brake is at it again:

news.sky.com/story/highway-code-stopping-distances...2

They may well be right (assuming the study is to be believed) regarding thinking time, but, aside from a few Morris Minors & Co still on the road, all modern cars (especially if fitted with tyres designed under 5 years ago) can almost certain stop in far shorter distances than the highway code says, so I would suspect the overall effect on the total stopping distance is negligable, or even reduced. Funny how that wasn't included in the 'study'.

I'm surprised they haven't advocated the government employing people with red flags walking in front of all vehicles to keep them at 'safe' speeds. I'm waiting to see if the Labour 'spokesperson' wades in on this (non-) issue to say that its an 'outrage' and 'demanding action' against the 'evil Tory/rich fast car owners'.

Edited by Engineer Andy on 25/07/2017 at 13:15

Braking distances - SLO76
Half the population live in a wee dream world behind the wheel with only half an eye on the road ahead. I'm horrified by the standard of driving I see daily on the road and from some friends and family who always sit too close to the vehicle in front or seem permanently in the wrong lane. I'd say the reaction times quoted here are even optimistic.

But yes the actual physical stopping distances beyond the reaction time are based on out of date information. I remember reading a test in either Auto Express or Autocar where they took a Mk I Ford Focus (without ABS if I remember right) and recreated the tests. The modern car stopped in half the distances at certain speeds and certainly far short of the official Highway Code figures.

I'd personally rather leave the greater distances in and add a bit extra in for the true reasction times if it scares a few new drivers into sitting at the right distance behind.

It's amazing how none of them can be told either. I'm quite polite with pointing out any safety related issues with family/friends driving me anywhere but you're almost guaranteed foaming mouthed abuse or at best a huffy silence if you suggest they get out of the fast lane at 45mph or sit more than 20cm away from the HGV in front.

It never ceases to amaze me when they hit the back of another vehicle yet still seek to blame anyone else but themselves. It doesn't matter what occurred to make that motor in front stop, you should be alert enough and far enough away to stop without hitting it. If you run into the back of someone you will be found at fault unless it was another impact at your rear that caused it.

Edited by SLO76 on 25/07/2017 at 13:33

Braking distances - Wackyracer

Completely agree SLO76, better brakes on cars have just resulted in drivers driving closer and closer to the car infront.

Braking distances - Andrew-T

It's interesting that the top illustration in that piece includes large warning road markings. In my experience those surfaces, or normal white lines, when wet can give noticeably less traction than plain tarmac or concrete. I don't know whether the Brake message talked about stopping in the wet, but in this country nothing explicit is said about it except for aquaplaning - extreme conditions - nor about driving at night.

Fifty years ago parts of North America posted road signs showing day speed limits, and night limits usually 10mph lower, with different reflective characteristics to emphasise the difference.

Braking distances - Vitesse6

It would be interesting to see some actual braking distances for modern cars, but the main thrust of the article is drivers reaction times.

Highway code assumes a reaction time of 0.7 seconds. How many people can actually achieve that. When I was at school doing a pre driving course we had our reaction times.measured. Most of us could manage 0.3 to 0.4 second. I don't think I could manage that now though.

An increase of 0.3 seconds in reaction time adds about 8 metres to the stopping distance at 60 mph.

Braking distances - oldroverboy.

I have an automatic safe distance warning on the passenger seat of my car. i can detect when she grips the armrests and hisses.

Braking distances - Stanb Sevento

I have an automatic safe distance warning on the passenger seat of my car. i can detect when she grips the armrests and hisses.

LOL

I have heard it said in the past that the best aid to raod safety would be a large spike mounted in the centre of every steering wheel.

Braking distances - galileo

It would be interesting to see some actual braking distances for modern cars, but the main thrust of the article is drivers reaction times.

Highway code assumes a reaction time of 0.7 seconds. How many people can actually achieve that. When I was at school doing a pre driving course we had our reaction times.measured. Most of us could manage 0.3 to 0.4 second. I don't think I could manage that now though.

An increase of 0.3 seconds in reaction time adds about 8 metres to the stopping distance at 60 mph.

There are a few 'reaction test' sites on-line, I have tried a few and my average is 0.28/0.34 seconds and I've been drawing State Pension for almost ten years.

Engineer Andy's post is absolutely spot on, road test results on modern cars show braking distances at most 2/3rd Highway Code distances, often much less.

The original 'thinking distances' assumed drivers were alert, sober, not drug users, not fiddling with mobile phones, not adjusting entertainment systems (radios were extra-cost options and needed a £1 radio licence!).

Braking distances - John F

Highway code assumes a reaction time of 0.7 seconds. How many people can actually achieve that. When I was at school doing a pre driving course we had our reaction times.measured. Most of us could manage 0.3 to 0.4 second. I don't think I could manage that now though.

Buried in my records is the printout of my BMW Fahrer-Training taken at a demo in Munich where we were watching tennis many years ago. At the age of 55 I managed 0.48secs and 62.3kg 'Bremskraft' before 'training', and 0.42secs and 93.3Kg after. So 0.7 probably about right for healthy OAPs.

Braking distances - Brit_in_Germany

There are reaction times and reaction times though. You may note the car in front braking because its lights have gone on and lift off the accelerator but then a further time is needed for that "oh s***" conclusion to be drawn and the brake pedal pushed to the floor. Automated braking is a wonderful invention though.

Braking distances - Cris_on_the_gas

OK so the stopping distances have remained unchanged since the 1950's. The efficiency of brakes has improved tremendously since then. However the human body has not evolved and now deals with a greater range of distractions.

Also the braking figures in the Highway code work on brake efficiency of 50%. Modern cars achieve much higher figures. However the to get an MoT pass, guess what the minimum efficiency is, yep 50%.

Braking distances - Bolt

Automated braking is a wonderful invention though

It certainly is, but should have been fitted to cars years ago for those who are distracted by a phone call/text message or someone walking in front of them (often happens now)

but maybe too many rely on automated braking on modern cars

Braking distances - Terry W

Reaction time is not the only factor impacting braking distance:

- tyres - new, part worn, on the limt, tread pattern

- road condition - wet, dry, worn and glazed, newly surfaced

- traffic volume may anyway compromise ideal vehicle separation.

I'm not sure stopping distances are of any relevance - tthe average driver is incapable of estimating distance with accuracy.

Or you could adopt the Clarkson wisdom - speed does not cause. accidents, accidents are caused by not stopping in time.

Braking distances - nick62

Reaction time is not the only factor impacting braking distance:

- tyres - new, part worn, on the limt, tread pattern

.

Never ceases to amaze me how many very new, expensive (and usually German) cars I see in the supermarket car park with bald tyres. I assume the ignorant owners just drive them until they fail the MoT? Not many spot checks carried out by plod these days afterall, (drove 400 miles to London and back yesterday and never saw one police car).

Braking distances - hillman

If any safety device is fitted to a vehicle some drivers will rely on it, not only new drivers either.

What we have to watch out for now-a-days is people walking out into the road while using mobile phones. I had one person walking on the pavement with their back to me turn onto a zebra crossing without looking or giving any sign. That must have been a very important phone call.

Tue 25 Jul 2017 14:46

Braking distances - bolt

Automated braking is a wonderful invention though

It certainly is, but should have been fitted to cars years ago for those who are distracted by a phone call/text message or someone walking in front of them (often happens now)

but maybe too many rely on automated braking on modern cars

Braking distances - badbusdriver

The highway code states a typical braking distance from 60mph as 240 feet. After a quick search, I found an article by motor trend, which is a US website/magazine, from 2015. This compiled their top 20 shortest braking distances from their road tests. The shortest distance recorded was by a 2014 corvette stingray roadster at 90 feet!.

Braking distances - badbusdriver

The highway code states a typical braking distance from 60mph as 240 feet. After a quick search, I found an article by motor trend, which is a US website/magazine, from 2015. This compiled their top 20 shortest braking distances from their road tests. The shortest distance recorded was by a 2014 corvette stingray roadster at 90 feet!.

OK, so a corvette is a high performance sports car with enormous brakes and tyres. So here is a more conventional comparison with the highway code braking distance from the autocar (dated 17/5/17) road test of the new suzuki swift in top of the range SZ5 spec and riding on 185/55x16 tyres.

Braking distance from 70mph according to the highway code is 96m (315'), the suzuki did it in 48.1m (157'9.7")

From 50mph according to the highway code is 53m (175'), the suzuki did it in 24.7m (81')

That is essentially half the distance!. So yes, maybe the highway code should be updated to show longer 'thinking time', but if so, it should also be updated to show the vastly shorter braking distances.

Braking distances - Manatee

K, so a corvette is a high performance sports car with enormous brakes and tyres. So here is a more conventional comparison with the highway code braking distance from the autocar (dated 17/5/17) road test of the new suzuki swift in top of the range SZ5 spec and riding on 185/55x16 tyres.

Braking distance from 70mph according to the highway code is 96m (315'), the suzuki did it in 48.1m (157'9.7")

From 50mph according to the highway code is 53m (175'), the suzuki did it in 24.7m (81')

That is essentially half the distance!. So yes, maybe the highway code should be updated to show longer 'thinking time', but if so, it should also be updated to show the vastly shorter braking distances.

The Highway Code's implied approach does not represent the real world, not because the reaction times and stopping distances are all wrong but because people don't generally drive by observing only the back of the vehicle in front (when they do of course, typically in fog, it all goes horribly and predictably wrong).

Most people, most of the time, are seeing beyind the vehicle in front. Occasionally this leads to its own problems, as with my wife when she looked ahead, saw the roundabout was clear, and srove straight into the car she had looked through/over/around!

If you are driving properly, you are not driving on your reactions anyway. In the event that something totally unexpected happens, and when reactions matter, most people just crash. The trick is to drive well enough that the unexpected is a very rare event.

Braking distances - Andrew-T

<< Never ceases to amaze me how many very new, expensive (and usually German) cars I see in the supermarket car park with bald tyres. I assume the ignorant owners just drive them until they fail the MoT? >>

Perhaps the owners have been driving long enough to expect that they will get 40K miles or even more from tyres. When cars were lighter (< 1 ton) with smaller, narrower tyres, 50K was not unusual. I think 20-30K is more normal nowadays, probably (my guess) because softer rubber with better grip wears out faster?

Braking distances - dadbif
“Only a fool breaks the two second rule”....
Braking distances - Engineer Andy

<< Never ceases to amaze me how many very new, expensive (and usually German) cars I see in the supermarket car park with bald tyres. I assume the ignorant owners just drive them until they fail the MoT? >>

Perhaps the owners have been driving long enough to expect that they will get 40K miles or even more from tyres. When cars were lighter (< 1 ton) with smaller, narrower tyres, 50K was not unusual. I think 20-30K is more normal nowadays, probably (my guess) because softer rubber with better grip wears out faster?

Quite possibly, though, like others' comments earlier about younger drivers driving within one car length of the one in front at high speed and thinking their car's new brakes (and ABS) will save them should they need to slam the anchors on, I see many people (especially younger drivers) drive their cars as if their life depended on it, or as if they are trying to achieve their car's 0-60mph time every time they accelerate away. I too also see many older higher performance cars (presumably owned by less well-off people hoping for some reflected status in their purchase) with tyres in poor condition.

I can still achieve decent mileages from a set of tyres - 50k or so from those (175/60 R13, slightly sporty) on my old mid 90s Micra, and 40k+ on my current Mazda3 (shod in 205/55 R16 tyres). As has been said, we just need to be reasonably (not Captain slow) light-footed, aware of other road users so we can reasonably anticipate future maneuvres, and calm so we don't give in to the red mist if and when we come across poor or reckless driving from others.

Braking distances - Andrew-T

Andy, your Micra reinforces my earlier point. Our now long-gone Pug 205 Dturbo managed about 50K on a set, but they had to be rotated periodically as the fronts wore about 3 times as fast as the rears because of the weight distribution and power steering.

Most modern cars have PAS and wide tyres, which must increase the wear rate of front tyres?

I don't think boy-racing is a particularly recent phenomenon though.

Edited by Andrew-T on 26/07/2017 at 10:56

Braking distances - Wackyracer

Most modern cars have PAS and wide tyres, which must increase the wear rate of front tyres?

Can I assume that the PAS comment on tyre wear is related to those people who dry steer? because I can't see any other reason why PAS would cause quicker tyre wear over non PAS steering.

Braking distances - Andrew-T

<< I can't see any other reason why PAS would cause quicker tyre wear over non PAS steering. >>

Surely because PAS can apply more force to turn the wheels than unassisted steering, where drivers have to take their corners more slowly (I'm talking mainly about slow manoeuvres such as parking, where PAS is most useful). Turning the wheels when stationary can strip tarmac, so tyre rubber won't be unaffected.

Braking distances - catsdad
re the 2 second rule mentioned above, this is a different but relevant issue. It takes into account that traffic is flowing and the car in front will not normally stop instantly. At 70 mph you cover a little over 200' in 2 seconds.
Reference has been made to the tests that show modern cars can stop in less than this distance. You might assume you could stop in the event of an immediate obstacle in your lane, such as debris, as long as you had 2 seconds clear view. I would suggest that in reality this is beyond many drivers in real life driving (as compared to being specifically prepared for a brake test). Braking in traffic from 70 mph in 200 feet to avoid hitting a pallet in the road is a real brown trouser moment.
Then when you consider that on a busy motorway the real gaps at 70 are likely to be a lot less than 200 feet and its easy to see why many accidents happen. Whatever the Highway Code might say and whatever a modern car can do in test conditions it pays to take a conservative view of the car and driver real life capabilities.