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PostPosted: Sat Mar 04, 2006 01:16 
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PeterE wrote:
SafeSpeed wrote:
ndp wrote:
All else being equal, the faster you go , the less time you have to react to hazards ahead and the less able you are to take controlled evasive action...

Nah. It's an illusion.

Drivers MAKE time to react. You can't give it to them.

And if you force drivers to travel significantly slower than they would choose to do, the extra time (and more) is just dissipated in inattention and distraction.


Could you cite for this?

And what do you do if a significant proportion of drivers are simply driving too fast?


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PostPosted: Sat Mar 04, 2006 01:27 
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ndp wrote:
SafeSpeed wrote:
ndp wrote:
All else being equal, the faster you go , the less time you have to react to hazards ahead and the less able you are to take controlled evasive action...


Nah. It's an illusion.

Drivers MAKE time to react. You can't give it to them.

See: http://www.safespeed.org.uk/timetoreact.html



From that link:

speed
If you have chosen the right speed to negotiate a hazard safely, speed does not contribute to time to react. This follows from forward planning. If the speed is too high to allow time to react then some other part of the safety system has failed.


So what to do when "some other part of the safety system has failed"?


Literally? Have an accident.

But more seriously, work to minimise the real underlying failures.

ndp wrote:
And as I have said - it isn't so much how people are failing, but why.


That's a very multilayered sort of question that's inherently difficult to answer.

I say at least 95% of all failures are due to shortfalls in skills, attitudes or sense-of-responsibility.

[the other 5% might include medical conditions, mechanical failures, etc]

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PostPosted: Sat Mar 04, 2006 01:33 
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ndp wrote:
And what do you do if a significant proportion of drivers are simply driving too fast?


Too fast for what?

What's a significant proportion? More than 10%?

Such conditions are indeed rare (given appropriate specification of the question) and are likely to call for a specific local solution. (Usually nicking boy racers who congregate as it happens.)

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PostPosted: Sat Mar 04, 2006 01:39 
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ndp wrote:
PeterE wrote:
SafeSpeed wrote:
ndp wrote:
All else being equal, the faster you go , the less time you have to react to hazards ahead and the less able you are to take controlled evasive action...

Nah. It's an illusion.

Drivers MAKE time to react. You can't give it to them.

And if you force drivers to travel significantly slower than they would choose to do, the extra time (and more) is just dissipated in inattention and distraction.

Could you cite for this?

Quote:
From Simonet & Wilde on risk homeostasis:

Due to the inevitable uncertainty of the outcome of any given action, the human brain has learned to optimise its degree of psycho-physiological arousal. A lower than optimal arousal would reduce our readiness to deal with a sudden threat; a higher than optimal level would soon exhaust our nervous resources. Physical risk, therefore, cannot be removed with impunity from the traffic system by a massive lowering of legal speed limits or any technical intervention aimed at the same effect. Such measures would be expected to produce a reduction in alertness and, hence, induce a state of behavioural adaptation to new conditions which is less capable of dealing with unexpected threats. A major decrease in the traffic accident rate per capita would, therefore, remain doubtful. If coercive speed reduction were successful in curtailing speed, this would likely amount to reversing the historical trend and thus lead to a reduced road mobility per head of population and a higher accident rate per kilometre driven.

Quoted some time ago by "teabelly", don't have original reference - search for his post.

Quote:
And what do you do if a significant proportion of drivers are simply driving too fast?

How do you define "too fast"?

The answer would often be to raise the speed limit or, if there genuinely are deceptive factors, make engineering changes to the road to reduce the perceived safe speed.

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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


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PostPosted: Sat Mar 04, 2006 02:05 
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ndp wrote:
Not at this time of night :)


Ok, I'm also off to bed now, anyway.

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Of course, the prosecutable threshold is 30mph - anything above this can be prosecutued.


Ok, let's just ignore the legalities and say 36mph - plain and simple.

Quote:
Depends on more than just speed.


Well, then let's examine the relationships between the relevant factors.

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PostPosted: Sat Mar 04, 2006 11:56 
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ndp wrote:
T2006 wrote:
ndp,

You fail to take into account the concept of 85th percentile speed, between 85-90th percentile speed you are at the lowest risk of accident.


Generally, yes.

What about at specific accident sites?



85th percentile speed is proven science. 'Safety' cameras are not.

Surely, the local speed camera partnership should have to demonstrate their effectiveness at such sites?

Or would evidence-based professionalism be too crazy a concept for them?


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PostPosted: Sat Mar 04, 2006 12:08 
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Any by evidence I mean independent, credible, valid statistical analysis performed by an unbiased individual.

Not 'spin' or propaganda reported by and organisation with a vested interest in proving their own self worth.

Think about it. For example: Schools aren't left to reivew their own effectiveness and performance; we have ofsted!


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PostPosted: Sat Mar 04, 2006 12:24 
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T2006 wrote:
Think about it. For example: Schools aren't left to reivew their own effectiveness and performance; we have ofsted!

Yeah... Right...

You could have picked a better example!! :lol:

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PostPosted: Sat Mar 04, 2006 20:34 
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SafeSpeed wrote:
ndp wrote:
SafeSpeed wrote:
ndp wrote:
All else being equal, the faster you go , the less time you have to react to hazards ahead and the less able you are to take controlled evasive action...


Nah. It's an illusion.

Drivers MAKE time to react. You can't give it to them.

See: http://www.safespeed.org.uk/timetoreact.html



From that link:

speed
If you have chosen the right speed to negotiate a hazard safely, speed does not contribute to time to react. This follows from forward planning. If the speed is too high to allow time to react then some other part of the safety system has failed.


So what to do when "some other part of the safety system has failed"?


Literally? Have an accident.


Thats simplistic. It is perfectly possible for one part of the system to fail but for no accident to result - be it through a good effort to recover by the driver who failed, good effort by others to recover, sheer good fortune or whatever.

Take the driver who (say) approaches a bend too fast, and the car starts to skid as a result. The driver may control the slide and get away with it, thus redeeming themselves and avoiding the accident - or they might not. Either way, they failed.

As we know from the principle of the accident pyramid, most accidents never happen - but this doesn't mean a failure hasn't occured.

So how to prevent such failures, especially where there is a site where a significant amount of drivers make similar failures (even if most don't result in accidents)?

Quote:
But more seriously, work to minimise the real underlying failures.


Agreed

Quote:
ndp wrote:
And as I have said - it isn't so much how people are failing, but why.


That's a very multilayered sort of question that's inherently difficult to answer.


Absolutely - and its one you to look at on a site-by-site basis - you can hypothesis at ones desk - but you cannot come to any meaningful conclusion without going out and looking.

Quote:
I say at least 95% of all failures are due to shortfalls in skills, attitudes or sense-of-responsibility.


Surely the road environment has an impact?

Quote:
[the other 5% might include medical conditions, mechanical failures, etc]


OK


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PostPosted: Sat Mar 04, 2006 20:53 
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T2006 wrote:
Any by evidence I mean independent, credible, valid statistical analysis performed by an unbiased individual.


Is there such an animal?

And why not analysis beyond statistical analysis?

Quote:
Not 'spin' or propaganda reported by and organisation with a vested interest in proving their own self worth.


How do you propose we sort the sheep from the goats?

Quote:
Think about it. For example: Schools aren't left to reivew their own effectiveness and performance; we have ofsted!


Perhaps an similar body would be a good thing wrt traffic engineering - however, would everyone accept its results if they disagreed with peoples beliefs?


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PostPosted: Sat Mar 04, 2006 20:55 
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ndp wrote:
SafeSpeed wrote:
ndp wrote:
So what to do when "some other part of the safety system has failed"?


Literally? Have an accident.


Thats simplistic....


Nah. That's a joke.

ndp wrote:
It is perfectly possible for one part of the system to fail but for no accident to result - be it through a good effort to recover by the driver who failed, good effort by others to recover, sheer good fortune or whatever.

Take the driver who (say) approaches a bend too fast, and the car starts to skid as a result. The driver may control the slide and get away with it, thus redeeming themselves and avoiding the accident - or they might not. Either way, they failed.

As we know from the principle of the accident pyramid, most accidents never happen - but this doesn't mean a failure hasn't occured.

So how to prevent such failures, especially where there is a site where a significant amount of drivers make similar failures (even if most don't result in accidents)?


Locally improve the environment (easier said than done, of course).

Nationally improve the drivers (equally, easier said than done).

ndp wrote:
Quote:
But more seriously, work to minimise the real underlying failures.


Agreed

Quote:
ndp wrote:
And as I have said - it isn't so much how people are failing, but why.


That's a very multilayered sort of question that's inherently difficult to answer.


Absolutely - and its one you to look at on a site-by-site basis - you can hypothesis at ones desk - but you cannot come to any meaningful conclusion without going out and looking.

Quote:
I say at least 95% of all failures are due to shortfalls in skills, attitudes or sense-of-responsibility.


Surely the road environment has an impact?


Yes. It can make road user mistakes more or less likely or it can make road user mistakes more or less tolerable (in the sense of 'fault tolerant' - an error that one 'gets away with').

But it's still road user error that causes each and every crash (except the odd medical or mechanical one).

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Our scrap speed cameras petition got over 28,000 sigs
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 Post subject:
PostPosted: Sat Mar 04, 2006 20:57 
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SafeSpeed wrote:
ndp wrote:
And what do you do if a significant proportion of drivers are simply driving too fast?


Too fast for what?


Quote:
What's a significant proportion? More than 10%?


Does it necessarily have to be that many?

Accidents are rare and random. The failures that lead up to them are also rare and random (if less so).

Quote:
Such conditions are indeed rare


So are accidents.

Quote:
(given appropriate specification of the question) and are likely to call for a specific local solution.


Yes

Quote:
(Usually nicking boy racers who congregate as it happens.)


Who said anything about boy racers?


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 Post subject:
PostPosted: Sat Mar 04, 2006 21:02 
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PeterE wrote:
ndp wrote:
PeterE wrote:
SafeSpeed wrote:
ndp wrote:
All else being equal, the faster you go , the less time you have to react to hazards ahead and the less able you are to take controlled evasive action...

Nah. It's an illusion.

Drivers MAKE time to react. You can't give it to them.

And if you force drivers to travel significantly slower than they would choose to do, the extra time (and more) is just dissipated in inattention and distraction.

Could you cite for this?

Quote:
From Simonet & Wilde on risk homeostasis:

Due to the inevitable uncertainty of the outcome of any given action, the human brain has learned to optimise its degree of psycho-physiological arousal. A lower than optimal arousal would reduce our readiness to deal with a sudden threat; a higher than optimal level would soon exhaust our nervous resources. Physical risk, therefore, cannot be removed with impunity from the traffic system by a massive lowering of legal speed limits or any technical intervention aimed at the same effect. Such measures would be expected to produce a reduction in alertness and, hence, induce a state of behavioural adaptation to new conditions which is less capable of dealing with unexpected threats. A major decrease in the traffic accident rate per capita would, therefore, remain doubtful. If coercive speed reduction were successful in curtailing speed, this would likely amount to reversing the historical trend and thus lead to a reduced road mobility per head of population and a higher accident rate per kilometre driven.

Quoted some time ago by "teabelly", don't have original reference - search for his post.


But thats all expectation - what has actually happened?

Quote:
Quote:
And what do you do if a significant proportion of drivers are simply driving too fast?

How do you define "too fast"?


Too fast being that their speed presents an unacceptable risk of an accident occuring and/or that the consequences of an accident occuring are unacceptably high.

Quote:
The answer would often be to raise the speed limit or,


Not by that definition of too fast.

If people are exceeding the speed limit but the risk and/or consequences presented by this are with acceptable levels, then the limit should be raised.

Quote:
if there genuinely are deceptive factors, make engineering changes to the road to reduce the perceived safe speed.


Certainly works better than legislative measures - but easier said than done though.


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PostPosted: Sat Mar 04, 2006 21:17 
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ndp wrote:
T2006 wrote:
Any by evidence I mean independent, credible, valid statistical analysis performed by an unbiased individual.


Is there such an animal?

And why not analysis beyond statistical analysis?

Quote:
Not 'spin' or propaganda reported by and organisation with a vested interest in proving their own self worth.


How do you propose we sort the sheep from the goats?

Quote:
Think about it. For example: Schools aren't left to reivew their own effectiveness and performance; we have ofsted!


Perhaps an similar body would be a good thing wrt traffic engineering - however, would everyone accept its results if they disagreed with peoples beliefs?


Clearly the concept of professional behaviour challenges you.

I must reiterate the importance of evidence-based practice in a situation like this.

It is important to remove bias or hidden agenda when evaluating effectiveness of a speed camera or SCP. Surely you agree with that?

I don't think sheep, goats or even squirrels have anything to do with statistical analysis.


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PostPosted: Sat Mar 04, 2006 21:22 
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PeterE wrote:
My theory is that Basingwerk is ndp's Dad :D


And my theory is that you are SafeSpeed's poodle :D

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PostPosted: Sat Mar 04, 2006 21:37 
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PeterE wrote:
the answer would often be to raise the speed limit or, if there genuinely are deceptive factors, make engineering changes to the road to reduce the perceived safe speed.


I have no quibbling with the first point - where it makes sense (and I don't merely mean for safety reasons), the limit should be raised.

As for the "engineering changes to the road", I have no problem with narrowing roads with stout iron or concrete bollards, as they have done in London. These are far scarier to perps than road humps, and many of them have lots of paint on them, showing that they creating employment in bodyshops!

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PostPosted: Sat Mar 04, 2006 22:46 
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ndp wrote:
SafeSpeed wrote:
ndp wrote:
And what do you do if a significant proportion of drivers are simply driving too fast?


Too fast for what?


Quote:
What's a significant proportion? More than 10%?


Does it necessarily have to be that many?

Accidents are rare and random. The failures that lead up to them are also rare and random (if less so).


Answers to my questions are needed.

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


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PostPosted: Sat Mar 04, 2006 22:55 
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ndp wrote:
PeterE wrote:
Quote:
From Simonet & Wilde on risk homeostasis:

Due to the inevitable uncertainty of the outcome of any given action, the human brain has learned to optimise its degree of psycho-physiological arousal. A lower than optimal arousal would reduce our readiness to deal with a sudden threat; a higher than optimal level would soon exhaust our nervous resources. Physical risk, therefore, cannot be removed with impunity from the traffic system by a massive lowering of legal speed limits or any technical intervention aimed at the same effect. Such measures would be expected to produce a reduction in alertness and, hence, induce a state of behavioural adaptation to new conditions which is less capable of dealing with unexpected threats. A major decrease in the traffic accident rate per capita would, therefore, remain doubtful. If coercive speed reduction were successful in curtailing speed, this would likely amount to reversing the historical trend and thus lead to a reduced road mobility per head of population and a higher accident rate per kilometre driven.

Quoted some time ago by "teabelly", don't have original reference - search for his post.

But thats all expectation - what has actually happened?

It just shows that it's a recognised behavioural phenomenon. And it does seem to accord with common sense, in that if you're forced to do something more slowly than you would otherwise choose to do so, your level of performance is unlikely to improve and may even deteriorate.

ndp wrote:
PeterE wrote:
How do you define "too fast"?

Too fast being that their speed presents an unacceptable risk of an accident occuring and/or that the consequences of an accident occuring are unacceptably high.

Are there really many roads like that, where there is an unusually high proportion of accidents that can be attributed to excess speed? The fact that the 85th percentile speed is well above the speed limit does not in itself mean that it's dangerous.

Also bear in mind that speed limits are set in large increments of 10 mph. Even if they're set properly, there will be 30 limits which would get limits of 36 or 37 mph if they were done in 1 mph increments. If the 85th percentile speed is around that level then in reality it might not cause any kind of problem and the best solution is simply to leave well alone.

Most speed enforcement occurs where speeding is least dangerous.

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


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PostPosted: Sat Mar 04, 2006 23:17 
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T2006 wrote:
It is important to remove bias or hidden agenda when evaluating effectiveness of a speed camera or SCP. Surely you agree with that?


Of course.

How do we propose we do that?

Quote:
I don't think sheep, goats or even squirrels have anything to do with statistical analysis.


Whoosh!


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PostPosted: Sat Mar 04, 2006 23:21 
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SafeSpeed wrote:
ndp wrote:
And what do you do if a significant proportion of drivers are simply driving too fast?

Too fast for what?

Apologies for missing this - but it happens I answered this when Peter asked this:

Too fast being that their speed presents an unacceptable risk of an accident occuring and/or that the consequences of an accident occuring are unacceptably high

Quote:
Quote:
What's a significant proportion? More than 10%?


Does it necessarily have to be that many?

Accidents are rare and random. The failures that lead up to them are also rare and random (if less so).


That would depend on the site and the other circumstances. There isn't a blanket answer.

Quote:
Answers to my questions are needed.


Until you answer my concerns regarding your analysis of 20mph zones, speed cameras in roadworks and reductions in fatalities on the continent, you are in no position to criticise in that regard.


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