weepej wrote:
Blaming a sharp corner for a death when it was clearly that the driver that took it too quickly is very different to blaming an uneven pavement for a trip.
Corners are features of roads, and wil be in the UK forever I suspect (and hope).
How did we get from "
concealed entrances, rises of road surfaces, muddy runoffs etc" to corners? I was talking about "hidden or unobvious hazards", not something corners can be described as; "
I cannot see the road". Surely you agree it is better to engineer out any unnecessary hazards, or provide adequate warning to drivers where that isn't possible?
How does making a road more dangerous make it more safe?
Why on earth would you want corners on roads, when the roads with the minimum of these - which just so happen to have the fastest speeds and apparently must have the most severe casualties (according to those obsessed with speed

) - happen to be the safest (those with the fewest KSIs per volume traffic) of all?
weepej wrote:
Sorry, I just can't get past a driver who comes off on a bend after losing grip has been nothing more than a little bit silly (except perhaps in exteme circumstances like a diesel spill, but even then the fater you're going the more violent the crash is going to be).
So why are motorways - the fastest roads - the safest?
Sure those who travel faster than they can stop in the distance they know to be clear (i.e. too fast for the conditions) are asking for it - but the folly of this isn't being communicated via these so-called public safety messages is it?
weepej wrote:
Steve wrote:
Do you agree or disagree that the other effects or bias on selection' and traffic displacement (on top of RTTM and long-term trends) must be accounted for before anyone can reasonably make any firm quantative (numerical) or qualitive (simply positive) claim about the effectiveness of speed cameras?
Is anybody else suggesting camera sites don't have a positive effect even after traffic displacement, RTTM and other effects are taken into account?
Do did you agree or disagree with the statement I gave? I've left the question buried within your quote so you can try again, unless you don't want to answer it? I don’t see how you can continue with that part of the debate if you don’t.
To answer your own question: I say that is quite likely given the comparative scale of 'bias on selection' relative to the remaining 10% 'scheme effect' fall at urban cameras sites - wouldn't you?
Getting back to the point: those who claim benefits from speed cameras do so without factoring in, or even mentioning, these critical and highly significant factors - is this morally right? (let alone technically right)
weepej wrote:
I think RTTM is not the be all and end all of removing "undesired" effects (and by undesired I mean a postive impact on the saftey of a stretch of road) from statistical analysis you would hope.
Of course not, that's why I also highlighted the factors of long-term trends, 'bias on selection' and traffic displacement (before even considering trafpol displacement). Don't all of those have to be considered before anyone can claim any positive effect? (how many times need I ask this).
Your "undersired positive" still has a large amount of illusion associated with it.
So did you understand the application of the RTTM effect to your motorway camera example: yes or no? (that was my question to you)
weepej wrote:
RTTM works both ways or might not be suitable to use at all. What if the increase number of crashes that led to the treatment weren't simply bad luck. Applying RTTM automatically might lead you to take a decision not to apply a treatement and that could be the wrong decision.
That's brilliant! Make the local environment more dangerous thereby justifying the installation of a camera - that's analogous to the london congestion charge (screw the light phasing, then use the high levels of congestion as justification for the rollout the charge). Even I wouldn't go that far!
How can 'Regression to the Mean' work both ways?
Perhaps there is the odd case of authorities making an area more dangerous, but I think we can all accept that the great majority of KSI accidents occurred where the roads weren't made more dangerous - unless you disagree with that?
weepej wrote:
I would think that's particulary likely on motorways.
How? Are there sections of motorways that have been altered to make them more dangerous (without the use of cameras) to attract significant KSI clusters? Please do explain that one.