Slow down call to save lives - and cash

[Paul Smith]

On Wed, 2 Apr 2003 23:24:41 +0100, John Openshaw <[email protected]> wrote:

>>>>Most importantly, I suggest that "Within the range of influence of any imaginable degree of
>>>>increased speed enforcement (using current technologies and enforcement systems) the correlation
>>>>between free travelling speeds and impact speeds is between zero and negative, except perhaps at
>>>>some very special accident black spot sites."

>I'm not one for pots and pans either so I had a look at the web-site, in particular the
>international graphs. You note that the deaths are on an exponential scale and the numbers are
>decreasing. As the numbers decrease so it takes a smaller number of deaths to change things
>dramatically (at least to the eye), and its not easy or even meaningful to draw conclusions.

But the size of the system is big and increasing, (greater number of vehicle kms) and that leads to
a remarkable degree of consistency from year to year. For example the last four years (-> 2001) GB
fatality figures are:

3421, 3423, 3409, 3450 (i.e. within about 0.6% of average)

But for an earlier four years in 1980 -> 1983

6010, 5846, 5934, 5445

I'm convinced we're at the "bottom" of a trend reversal.

>For example, if you plot a hypothetical line (log or lin domain makes no difference), using any
>recognised line fitting technique, what is the confidence level at which your observations take
>place? In fact, I'm surprised to see that your in-depth numerical analysis omits error bars, as
>these could quite easily invalidate/validate everything you say.

Sadly, as of now, I don't know how to do that.

>As far as the web-site goes, you say, and I paraphrase: 'the graphs go wonky at a certain date, and
>this date coincides with speed cameras, ergo there is a link'. Unfortunately you do not prove
>statistically the graphs go wonky, and there is no evidence on your site of a causal link between
>speed cameras and fatal accidents.

I certainly don't say "ergo there is a link". I do say it's the only explanation I've got which fits
the observed effect, and I did predict the effect long before I found anything in the data to
support it.

I look forward to proving that the "graphs go wonky".

As for proving a causal link, that would be hard indeed even with unlimited resources, given the
proposed mechanism:

http://www.safespeed.org.uk/tiger.html

I certainly don't expect to be able to prove causality.

>So one question I would like answered as I cant see it is: You say that the death rates have either
>increased or decreased (according to speed kills campaigns) - what is the confidence interval for
>your hypothesis for all the international graphs? Is it 99%, 95% or what?

I'm working on all of this, John. I've purchased 4 text books about statistics, and I'm learning
stuff that I've forgotten from 30 years ago when I last used it. It certainly doesn't help that
Excel is a seriously **** statistics tool and tends to lead one astray. I just love Microsoft.
--
Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
cameras cost lives

 

[Paul Smith]

On Wed, 2 Apr 2003 22:43:19 +0000 (UTC), "W K" <[email protected]> wrote:

>> Most importantly, I suggest that "Within the range of influence of any imaginable degree of
>> increased speed enforcement (using current technologies and enforcement systems) the correlation
>> between free travelling speeds and impact speeds is between zero and negative, except perhaps at
>> some very special accident black spot sites."

>Perhaps "people on the whole judge their 'safe' speed fairly well, but leave greater margins for
>error in places with lower hazard densities" ... "where hazard densities are random and unexpected,
>and have a low possibility of happening, people ignore this in their choice of speed" ie people
>drive too fast in towns.

New research from Virginia (which I'm waiting to receive in the mail) concludes that 95% of
accidents are due to inattention or distraction in one form or another. Such a view fits my
understanding of how accidents happen. You mental model sees speed (can't stop in time) as an
accident cause, but that just does not fit reality. If it did we'd see an approximate fourth power
relationship between free travailing speed and fatality percentage.

>> i.e Excessive speed enforcement tends to increase accident severity.

>By what mechanisms? Apart from ones in your imagination based around stupid and 2 dimensional women
>that you can conjure up in your imagination.

By the mechanism of messing up driver priorities.
--
Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
cameras cost lives

 

[Mr R@T \ -Lsqco]

In news:[email protected], Dave Kahn <[email protected]> typed:

> cyclists wouldn't go that far, and by extension you would also have to ban cycling as cyclists
> sometimes hurt themselves or each other or pedestrians without the help of motor vehicles.

And you would have to ban *pedestrians* as well, as if people go out they may be tempted to drink or
take drugs and then beat up or rob one another, or might just be clumsy and trip over things. This
also costs the NHS money.....

Alex

 

[W K]

"Paul Smith" <[email protected]> wrote in message

> You mental model sees speed (can't stop in time) as an accident cause, but that just does not fit
> reality.

It does fit reality - but luckily we do judge it fairly well on the whole. Do you know anyone who
drives the same speed whatever the hazard density.

> If it did we'd see an approximate fourth power relationship between free travailing speed and
> fatality percentage.

It would if people did not choose their speed in terms of hazard density.

What is more dangerous? A baseball bat, a handgun or a nuclear weapon?

I'd suggest the fatatlity rate for them is 1>2>3.

 

[Marc]

wafflycathcsdirtycatlitter <[email protected]> wrote:

> Ye gods, Simon, it doesn't take the resident ar*ehole long from chipping in with his usual drivel,
> does it. The man should be sectioned ;-)

Into how many pieces?

--
Marc Tabards, banners and signs for fundraising events and charities
http://www.jaceeprint.demon.co.uk/