Safe Speed Forums

Yep, you have to be able to stop within the distance that you know to be clear - but you must also observe way beyond the vehicle in front.

The two are fully compatible - you need to know that the vehicle in front will clear your safe braking zone before you need to occupy it. It's all perfectly normal actually...

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Does being understandable stop it being incongruous? It doesn't for me.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

Ah, I see the misunderstanding, I should have said stopping distance not braking distance, I knew what I meant while I was typing it

Most engineering is done in SI units - which means distances in metres.
Speed should, by the same token, really be in km/h, but we use mph in this country so I use mph so everyone can identify with it.

Cheers
Peter

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Only when ideology, prejudice and dogma are set aside does the truth emerge - Kepler

That tallies with what I saw in Anglesey. Locals "in the know" rigidly obeying speed limits, due to draconian speed limit enforcement and cunningly placed Talivans. Tourists not "in the know" get impatient with being stuck in long queues of slow drivers, take risks, and overtake somewhere at best inappropriate and at worst dangerous. Every so often it turns out to a risk too far.

Of course the fatal smashes are seldom anywhere near the camera locations, which are placed to maximise revenue rather than address specific safety issues. (One on the Menai Bridge - Amlwch road is on a dead straight NSL section with no obvious hazards in either direction as far as the eye can see - in other words an ideal "overtaking straight" - indeed one of the few points on that road where it is safe to overtake a queue of vehicles.) And as - they argue - the fatal smashes are clearly solely due to "excessive speed", they are then used to reinforce the flawed argument that excessive speed is the sole cause of accidents, and hence as justification for their enforcement policy.

For interest, just derived a table of stopping distance (from highway code) vs 2 sec distance (using full stops instead of spaces because it seems to strip multiple spaces out).

Speed(mph).....Stopping Distance(m).....2 sec distance(m)
......20........................12...............................18
......30........................23...............................27
......40........................36...............................36
......50........................53...............................45
......60........................73...............................54
......70........................96...............................63

As you can see, if cars are separated by stopping distance rather than 2 sec distance, the separation will increase much more with speed, leading to reduced throughput at higher speeds compared to 2 sec separation.

Many modern vehicles block your view of the road ahead, so in these cases a stopping distance gap would be more appropriate than a 2 sec gap.

It's rare indeed not to be able to observe past the vehicle ahead.

And don't forget what we need to observe for - the sort of thing we need to know doesn't exist is the sort of thing that can give a stop in less than a braking distance - stationary traffic for example.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

If you're strictly using SI units, then speed should be in m/s (metres per second)

There is a strong argument for the voluntary use of metric measurements.

There is no argument save that of the jackboot for enforcing their use via the criminal law.

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"Show me someone who says that they have never exceeded a speed limit, and I'll show you a liar, or a menace." (Austin Williams - Director, Transport Research Group)

Any views expressed in this post are personal opinions and may not represent the views of Safe Speed

But, besides anything else, by and large drivers do not drive according to stopping distance, so - in ther real world - throughput cannot have any relationship to speed.

In fact, there is a tendency for traffic to bunch up at lower speeds on the motorway - which temporarily increases throughput.
But when traffic is bunched up then small perturbations, overreactions etc are much more likely to bring the traffic to a complete stop - at which point the throughput falls to zero.

Cheers
Peter

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Only when ideology, prejudice and dogma are set aside does the truth emerge - Kepler

This is something on which meaningful research could be done - to study motorway situations with very high traffic flow and establish the real-world separation times.

I suspect as traffic goes slower drivers do instinctively reduce the separation times, but as motorway traffic rarely flows smoothly below about 40 mph it may be hard to derive firm conclusions.

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"Show me someone who says that they have never exceeded a speed limit, and I'll show you a liar, or a menace." (Austin Williams - Director, Transport Research Group)

Any views expressed in this post are personal opinions and may not represent the views of Safe Speed

Paul you amaze me

What about the speedo check - so often necessary when the scamerati are about!

Cheers, Chris.

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Stultus est sicut stultus facit - a known fact
Stercus accidit - a truism!