Chris Tolley (ukonline really) gurgled happily,
sounding much like they were saying:

This may come as a shock to you, but the tables never had anything
to do with real performance. They are a simple mathematical model
linking the speed in mph with the stopping distance in feet. Anyone
with GCSE maths should take no more than 2 minutes to deduce the
formula that is used..

Sure. But the formula was based on a roughly representative family
car of the period - the 105E Anglia, allegedly.

The formula is far too simple to be based on anything real.

No, but the formula would have been worked so that the resulting
stopping distances are approximately correct for "something real".

Perhaps you should offer some evidence for this contention.

Put it this way - I didn't bother to memorise the distances for my
driving test. I memorised the formula, and as I say, it links mph to
feet. The only way in which it would have any resemblance to reality is
if there were some universal driving constant whose value happens to lie
in the region of 1/5280, being the conversion factor from miles to feet.

So did this formula get plucked from thin air for a totally random result?

Why 75m from 70mph?
Why not 200m or 20m?

It no doubt gives and always gave a safety margin. But until every
relevant vehicle has ABS

Which doesn't actually make the slightest difference to stopping
distances, since it does absolutely nothing at all unless the driver
cocks up in a way that would have failed them their driving test.

Never having had a car so fitted, I wouldn't know. The only evidence I
have to go by is that the continuous rubber smears on the road tend to
be longer than that dashed ones, from which I infer that ABS reduces
stopping distances.

Did you miss the "unless"?

Personally, I drive according to the two second rule. That's much more
straightforward. I observe that many of my fellow road users think they
are considerably better drivers and can get away with a 0.5 second rule.

I don't think anybody's said anything to contradict that.

But if these figures purport to be a typical "stopping distance", do you
not think it might actually be useful if they were?