Re: Totally OT - Highway Question - Is 100 Metres Enough

The message from John Rumm contains these words:

I don't think they have changed (other than the units) for a good bit longer than that.

I can't find a single copy of The Highway Code atm (I have 3 stretching back over the later half of my driving experience) but ISTR that the formula is 0.5 seconds thinking distance plus retardation at two thirds g. I wouldn't doubt halving the thinking distance but retardation well in excess of g from an ordinary road car seems a little suspect to me. IIRC brake efficiency for cars only needs to be 50% so was it that that was doubled?

Reply to
Roger
Loading thread data ...

And so would my morris 1100. Under perfect conditions. As probably were your tests. "Accidents" occur when some conditions (which includes driver attitude) are less than perfect. Allowances must be made for such conditions. Most drivers are incapable of making perfect decisions at all times, they may be tired, have had a row, it may be raining etc....

A safety margin is essential. 100% doesn't seem excessive.

Reply to
<me9

formatting link
the units in which I learned to drive,

stopping distance (ft) = v(1+v/20) where v is the speed in mph

or v + v^2/20 thinking time approx 2/3 second and 0.6G ?

Reply to
Tony Bryer

Then why was it not included in the original figures for the vehicles current at the time then? ;-)

Reply to
John Rumm

Its probably more to do with the requirements of the MOT which only require

0.5G. Cr@p really, mine stalled the rolling road when they were done three weeks ago.
Reply to
dennis

The message from Tony Bryer contains these words:

Perhaps it was the braking test I was thinking of, not thinking distance. :-)

I have now found 2 of my Highway Codes and the earlier one copyright

1978 still has the figures in feet. Thinking distance is conveniently is one foot per mph and braking distance at 30 mph is 45 feet - 0.67% g. The metric equivalents of 9m and 14m translate to 29.5 feet and 45.9 feet so the metric equivalents are a bit of a fudge, but then so probably were the original figures.
Reply to
Roger

So 40mph on a not particulary busy motorway is OK then?

Reply to
Dave Liquorice

formatting link
would be the (in)famous page:

formatting link
back over the later half of my driving experience) but ISTR that the

Many modern cars can pull over 0.6g in a corner, they can usually stop much better than that.

Most bods who tried found they could stop in the dry within 55m including thinking time. If you accept the highway code thinking distance at 70mph (31m/sec) being 21m, then that only leaves 32m to actually stop in.

In g terms that gives us:

v^2 = u^2 - 2as

a = (v^2 - u^2) / -2s

a = (0 - 31^2) / -64

15 m/sec^2 or about 1.5g

(It maybe that their thinking time in these tests was less than in real life because they were anticipating the event).

Reply to
John Rumm

Its more than the legal minimum and large vehicles on motorways do less than that at times.

I take it you don't see them when you drive on the motorways.. asleep maybe?

Reply to
dennis

Indeed.

However to exactly keep within a speed limit means spending most of your time on cruise control or looking at the speedo all the time. Hardly conducive to safety.

Reply to
The Natural Philosopher

Does.

You pull out in front of another car, driving very slowly, and watch what happens..

You try dreiving non stop to teh other end of teh country at 20mph, and see hwo tired you get, and how many accidents you cause.

No, its the trees leaping out in front of you, stupid.

>
Reply to
The Natural Philosopher

The message from John Rumm contains these words:

The handbooks for the 60s/70s Lotus Elan and Plus 2 contain the following:

"capable of exceeding .9g retardation" and "capable of exceeding .8g lateral side load".

Were they really 40 years in advance of their time? :-)

My money is on them ignoring thinking time completely.

Reply to
Roger

Ive got no problem with anyone doing that If its uncrowded. Ive done 25mph down the M1 towing about 2 tons up a steep hill.

I have to say that the tailbacks it caused were embarrassing and frightening.

Although not illegal it was in my opinion dangerous.

An accident is caused by tow objects at different velocities occupying te same space. Whether one is too fast, or the other too slow, or both in the wrong place, is open to endless argument.

However the fact remains that if you insist of travelling at a vastly different rate from those around you, you are a de facto hazard to them.

If you decide to drive down a mortorway at 40mph, the only safe thing is for everyone else to drop to that speed. You MAY consider that is precisely what should happen, but the days when everyone else magically conformed to YOUR opinion were left behind the moment your mother whipped her tit out of your mouth.

Reply to
The Natural Philosopher

Which is permanently switched off because they think they are driving slowly..

I have never had an accident when exceeding a speed limit..

Reply to
The Natural Philosopher

IF you are a habitual fast driver thinking distance is about 0.2 seconds or less.

However 0.6g is pretty fair..many trucks and vans won't do that..many sports cars will do .8-1g or so..but few more than that.

Reply to
The Natural Philosopher

In the days when I first saw that,a Morris 1100 was a pretty modern car. Now my cousins sit up and beg ford popular with cable brakes on oversized crossply motorcyle tyres..was a different thing altogether.

Even then they had to write rules for idiots in crap cars. But in those days they weren't enforced for intelligent people in decent cars, by Big Brother cameras.

Reply to
The Natural Philosopher

Yep. At least with a horse you can blame someone. Deer you can't.

Reply to
The Natural Philosopher

that are largely unenforced.

Reply to
The Natural Philosopher

What legal minimum, references please?

I've yet to see any signage that there is a minimum limit on entering a motorway or the end of a minimum limit when leaving. Indeed minimum speed limits are very rare in the UK.

Not very often, these days most wagons sit at 56mph on the limiter no matter the gradient. Other large vehicles, mobile cranes etc, have flashing orange beacons and/or an escort.

No, at least not wagons or large vehicles without beacons. The dangerous ones are ordinary cars doing 40mph.

Reply to
Dave Liquorice

Luck. Do I take it that you have had an accident while driving below a speed limit?

Reply to
dennis

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.