Safe Speed Forums

I think we know the correlation is the U shaped curve of Solomon et al. But it isn't because of speed. It's a cause in common.

Average and soemewhat faster than average competent drivers cope with the bend well.

Slower than average incompetents crash on the bend more often.

Much faster than average nutters crash on the bend a fair bit because they are nutters.

Much faster than average experts hardly ever crash on the bend.

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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

This report is quite critical of Solomon's work, and describes a study where they attempt to address those weaknesses:
http://www.atsb.gov.au/road/rpts/cr204/index.cfm
They conclude that increased speed simply increases accident risk, they don't find a U curve relationship.
However, they still make what I consider a mistake in that they consider the speed of the vehicle at the start of the accident event period rather than free travelling speed much earlier, but if this were going to bias the results, it would make it more likely to show that slower drivers are more dangerous, and as this wasn't part of the findings I'm not too concerned.

See this page:
http://www.safespeed.org.uk/speedlimits.html

Which I think bridges the gap.

I believe the work that shows risk increasing with speeds is coloured by over simplified pre-existing beliefs.

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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

The assertion in the link I gave ( http://www.atsb.gov.au/road/rpts/cr204/index.cfm ) is that it is Solomon's approach which is over simplified, and they tried to address the simplifications that led to the bulge at lower speeds. When Solomon's simplistic assumptions are addressed with a more complex study, they found that the lower speed bulge disappears. Of course, there might be even more complexity required to get a true result, which might be different again, like in my example I posted once of investigating a link between car colour and likelihood of crash, where I was able to keep giving out additional facts that reversed the result each time.

Nah, the Kloeden report is just crap or even twisted crap. John Lambert re-analysed their data and the U shaped curve reappeared as usual.

Anyway, see my reference - the idea that a car at 20mph in L3 of a motorway doesn't have an elevated crash risk is just absurd.

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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

They then go on to rebut Lambert's rebuttal:
http://casr.adelaide.edu.au/speed/LambertReply.pdf
This includes addressing the "20mph in L3" point, where their argument is that they simply didn't see many such crashes, so it can't be a significant factor.

Yeah - but that's after they have proved themselves to be liars and twisters of fact... Or maybe it's just a firm belief that road safety 'must be' a problem in physics (which clearly it cannot be).

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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

This is a very fundamental mistake on their part.
They only consider the accident event period, and then attempt to change just one parameter - ie speed - and leave everything else unchanged. What this means is that if, at the start of the event period, ie when the driver first realises the need to take action, you simply change the speed then you change the outcome of the accident - a lower speed would result in either a lower intensity collision or none at all.
But one cannot change the speed at the start of the event period without affecting everything else about the event period - the laws of physics do not allow this.
I've had correspondence with one of the outhors of those reports, and he denies that they make such an assumption - yet it's very clear from their papers that they do.

Cheers
Peter

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

It's also worth noting that none of these studies tell you anything at all about what you should set the speed limit to be. They show the risk associated with travelling at different speeds in the context of the current speed limit and speeds of other vehicles, but if you could speed up or slow down all the vehicles on the road, that doesn't mean they would take on the risk associated with their new speed in the previous environmental context.

I'm coming late to this so if I'm way off track then give me a sound beating.

Stevei, am I correct in my understanding that your figures suggest that 'speeding' vehicles have fewer accidents than 'non speeding' vehicles?

If this is the case then I think the answer lies in the soft fleshy component behind the wheel.

I would put forward the hypothesis that those who adherre strictly and unswervingly to the speed limits do so because they have an inherrent lack of confidence and are unable (or inexperienced) to deal with changing environments. Therefore when conditions change on the road (for any one of a number of reasons) they are more prone to accidents.

In my experience the worst drivers I have encountered are the ones who refuse to exceed the limit.

Further to this I would suggest (based on nothing but suspicion) that of those 'speeding' drivers who have accidents a high proportion will be inherrently reckless (non insurance, poorly maintained vehicles, drink/drugs etc)

My brother was a helicopter pilot (AAC) and a fundamental part of the early selection revolves around, multitasking and hazard perception and so on. Some people are simply better at it than others. He passed his basic training but failed when it came to battle training reasons - failing to deal with the changing environment, ability to predict, multi tasking etc. (So far as I am aware there is no speed limit for helicopters)

No, I was just taking Paul's figures from this statement:
"Only about 1% of crashes involve an otherwise responsible motorists in excess of a speed limit, yet 60% of motorists are speeding at sample sites in free flowing conditions."
And plugging them into the relevant statistical equations, however it's wrong to do so because we need to correct for potential differences in conditions between when the free flowing traffic data is collected, and when accidents happen. Some studies have purported to do this, but none have done it in quite what I consider the right way, so the question can't in fact be answered at present.

However, regarding what you were saying about some people just being better at processing all the information while driving along, I think the simplest demonstration of this is the difference between people in playing driving games on a computer. E.g. I can play Gran Turismo far better than a friend of mine - I drive faster and crash less than she does when playing it. This is mirrored in real-life driving, where I don't have accidents, and she has minor accidents fairly frequently.

A really good game to illustrate this is Need For Speed Underground 2, where you have to do "real" driving in between races, to get from venue to venue. It's really quite remarkable just how fast you can drive, yet never crash, provided you adhere to the rule of always being able to stop in the distance you can guarantee to be clear. It means that you accelerate and decelerate rapidly a lot, but provided you scrub the speed off when the hazard first appears, and keep your speed down to a level where you can always scrub enough speed off in time if a hazard appears at the limit of your vision, you're safe, even though you might be travelling at many times what the legal speed limit would be in real life.

This really is the pointer to the crux of the matter.

We've got this closed loop: risk affects speed affects risk.

We vary speed where hazards exist to manage the risk posed by the hazards. This works in the vast majority of cases, and we know it does because crashes are rare, yet if we stopped managing speed in this way we'd crash very quickly.

The speed camera programme doesn't assist this process - it hinders it.

Road safety entirely depends on the existence and performance of this closed loop, so it's no surprise that speed cameras aren't delivering good results.

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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