Re: Advice about speeding ticket please

On Fri, 6 Apr 2007 16:36:58 +0100, Norman Wells
<norman@xxxxxxxxxxxxxxxxx> wrote:

<snip>


Assuming we are not concerned about large blocks of concrete or
something dropping from the sky a driver can brake and slow down more or
less as quickly as the traffic in front of him. The safe following distance
is all to do with reaction time not braking distances.

According to the Highway Code:

"105: Drive at a speed that will allow you to stop well within the
distance you can see to be clear. You should leave enough space between
you and the vehicle in front so that you can pull up safely if it
suddenly slows down or stops. The safe rule is never to get closer than
the overall stopping distance."


They missed "but stupid" after "safe".

Yes, that is indeed "the safe rule", but it is also a ridiculous
distance to keep as a gap in normal motorway traffic.

And that is even without taking into account the ridiculously out of
date stopping distances given.


At 30mph the overall stopping distance is given as 75ft. At 60mph, it
has risen over three times that to 240ft.

All the motoring organisations, and the police recommend a 2 second
gap at any speed above 40mph. 2 seconds is quite a bit less than 80
yards at 60mph (in fact it is just under 60 yards).


If drivers follow the 2 second rule (which is independent of speed) then
the flow rate of any lane of traffic is one per 2 seconds + the time the
vehicle takes to travel its own length. That time reduces as vehicle speed
increases without limit.

Indeed it does, and so too does the risk to life and limb. The 2 second
'rule' is actually ridiculously independent of the physics of moving
masses which, if your education ever got that far, would have taught you
that the energy possessed by that mass increases as the square of the
velocity. And it's that energy that has to be dissipated by the brakes.
As they can only dissipate a certain amount of energy per second, the
braking distance increases in proportion to the square of the velocity.

As an example, I'm sure you wouldn't be too happy to be followed on a
German autobahn by someone doing 150mph if he's just 2 seconds behind
you.

Why on earth not?

Assuming of course that you are also doing 150mph.

You can't stop significantly quicker than he can unless you do so by
hitting something.


The only other (and more significant) way flow rate can be increased is by
drivers sacrificing the 2 second rule, they may be more prepared to do that
at moderate speeds.

It depends what you mean by moderate speeds. At 40mph, the overall
stopping distance is virtually the same as you would leave under the 2
second rule. However, that rule becomes increasingly reckless the
higher the speed.

It never becomes reckless at the speeds experienced on UK motorways
(including "reasonable" speeding drivers).


--
Alex Heney, Global Villager
All things are green unless they are not.
To reply by email, my address is alexATheneyDOTplusDOTcom
.

Relevant Pages

  • Re: Advice about speeding ticket please
    ... but then it never actually suggest you should leave a gap equal ... "Drive at a speed that will allow you to stop well within the distance ... The 2 second rule has no such scientific foundation, ... speeds over about 40mph. ...
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  • Re: Advice about speeding ticket please
    ... strictly enforced speed limit then they can do nothing to reduce gaps ... four times the distance apart. ... at moderate speeds. ... the overall stopping distance is virtually the same as you would leave under the 2 second rule. ...
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  • Re: Advice about speeding ticket please
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