Stopping Distances ?

[osprey]

Does anyone know when the calculations regarding stopping distances were done and if they have ever been revised to take into account all the new technology to have occurred since their original adoption?

[Panic Button]

From what I see every day on the M25, no one takes a blind bit of notice anyway.

Its like a Newton's cradle some days, with lines of cars shunted into eachother.

[ABerrant]

I believe Stopping Distances were formulated in the 1930s and certainly appear in the 1946 edition of the Highway Code.

http://normandyhistor...co.uk/library/hwc.pdf

The figures remained unchanged until the conversion to metric units whereby slight differences were introduced due to the feet values having been rounded to the nearest metre.

http://www.direct.gov...alasset/dg_070645.pdf

Granted that brake, tyre, road surface etc. technology has advanced and has surely shortened the Braking Distance but I tend to think that with the increased distraction and careless attitude of many drivers compared to that of decades ago, the Thinking Distance has probably increased to counteract any need to revise the "Typical" Overall Stopping Distance.

[R1Geezer]

As is occasionally pointed out on motoring shows they were calculated in the early days of the highway code (1930's)when 70 was more than a lot of cars could even manage and brakes were much worse. One test Clarkson did was with the supposed distance for 70mph (315 feet) he set ou cones to indicate 160 feet and then managed to stop on that distance from 140mph. Essentially with modern cars the distances are much much less.

[ABerrant]

When debating "Typical" Stopping Distances I am not sure how the much reduced braking distance of a supercar such as the Mercedes-Benz SLR McLaren (as tested by Clarkson), with its Sensotronic braking system, carbon-ceramic front discs and automatic air brake, is meant to equate to the more usual runabouts found on British roads.

Limiting the argument to more mundane modern roadcars will still prove the point of improved nominal braking performance over their ancient forebears, but factors such as any reduction in brake efficiency (legal minimum 50%) should not be ignored.

We should also factor in the increased reaction times for those drivers who are allowed on the road while seemingly oblivious to all around them. If we take 60mph as an example:

60mph = 18m (Thinking) + 55m (Braking)

Another Clarkson test (Cheap Car Challenge) showed a road legal Rover 416 reduce the 55m braking distance to 44m. It would only need a driver to react 0.4 seconds slower than the "typical" driver to travel those 11m.

[Marijn]

Stopping distances aren't in URGENT need of revision, unless of course we've under estimated the stopping distance. Why do people like driving so close to each other anyway, don't they want to see around to see what's happening further up the road? Or do they just enjoy intimidating people. They don't get to their destination much quicker by being half a second closer to the car infront!

[ABerrant]

The "Thinking Distance" is based on a response time of 0.68 seconds. The response time includes processes such as recognising a situation, deciding the appropriate action, putting that action into effect (e.g. object appear in road ahead, object to be avoided, move foot from accelerator to brake and depress pedal). However, there is not a simple calculation for the response time that covers every driver in every situation under all conditions. The figure should be high enough to err on the side of caution and allow for drivers with lesser capabilities since they are allowed to use the roads unhindered.

Many studies over many years in many countries have tested response times. TRL car simulator tests have shown a typical "expected event" response to take around 0.85 seconds; unexpected events, of course, lead to longer response times. US Highway Design test protocols uses an ultra cautious standard response time of 2.5 seconds and Australia plumps for their average time of 1.5 seconds.

If the UK was to adopt 1.4 seconds as a reasonable response time this would see Thinking Distance double, and if brake technology has reduced typical Braking Distance to 70% of the old value (which I doubt is true for a significant number of road legal cars with more than one occupant) how would Stopping Distances compare?

Old ... 30mph = 9m + 14m = 23m
New... 30mph = 18m + 20m = 38m

Old ... 60mph = 18m + 55m = 73m
New... 60mph = 36m + 38m = 74m

Old ... 70mph = 21m + 75m = 96m
New... 70mph = 42m + 52m = 94m

I suspect not the results expected by advocates of Stopping Distance reform.

[ABerrant]

Oops! Typo in first calculation...

Old ... 30mph = 9m + 14m = 23m
New... 30mph = 18m + 10m = 28m

[Muppit]

For arguements sake, if stopping distances were reduced, by a few metres say, does that mean that when you see a child run out in front of you, you would think it's ok, I've got another few metres to go as yet...

Of course not, learning stopping distances is just a way to try and make new drivers learn that they can not stop on a sixpence. Who cares what the numbers are, if you see a hazard just try your best to avoid it!!!

And in answer to your question... apparently not.

[flip_flop]

I couldn't tell you the stopping distances in the Highway Code if my life depended on it, and I suspect I am in the majority - so to a large degree I think they are pretty irrelevent anyway.