Safespeed spoilsports

[Robert McDonald]

> Colin, if drivers were only driving at 12mph they would be completely asleep and driving off
> bridges, into canals etc all the time.

Sooooo... Everyone in cities where the average speed is around 12 mph all crash before they reach
their destination? Or do I just not understand the maths at DeathSpeed?

BigRab

 

[Robert McDonald]

> The point that crash energy equivalent to 12 mph crashes is all that's needed to kill the number
> we DO kill, speaks volumes about the importance of speed in fatal accidents.

Can someone *please* enlighten me? If I run into a house at 12 mph with my car the , presumably, the
delta V is 12 mph? No-one in the car (wearing seatbelts)would die under these circumstances from
injuries sustained in such an impact.

Anyway, it's completely wrong to speak of 'energy equivalents' at a specific velocity without any
mention of mass.

BigRab

 

[Paul Smith]

On Thu, 27 Feb 2003 10:01:44 -0000, Colin Blackburn <[email protected]> wrote:

>> Perhaps you would like to stop spouting hot air and identify an incorrect statement on the page?

>The conclusion is incorrect. I've already said. All that you have done is calculate a possible
>average value for delta V for UK statistics. You then cunningly allow delta V to become V and draw
>an erroneous conclusion. What more can I say.

It certainly isn't meant to be "cunning". It's supposed to be clear and transparent. I'll see what I
can do to clarify that point.
--
Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
cameras cost lives

 

[Colin Blackburn]

In article <[email protected]>,
[email protected] says...
> On Thu, 27 Feb 2003 10:01:44 -0000, Colin Blackburn <[email protected]> wrote:
>
> >> Perhaps you would like to stop spouting hot air and identify an incorrect statement on the
> >> page?
>
> >The conclusion is incorrect. I've already said. All that you have done is calculate a possible
> >average value for delta V for UK statistics. You then cunningly allow delta V to become V and
> >draw an erroneous conclusion. What more can I say.
>
> It certainly isn't meant to be "cunning". It's supposed to be clear and transparent. I'll see what
> I can do to clarify that point.

What point? The point is there is no point to be drawn from what you have done.

You have stated, in conclusion, that if there was a rigorously enforced 12mph speed limit the death
toll could be the same as it is now, this is where delta V has become V.

What the numbers are telling you, in fact, is that if the average delta V is around 12mph the death
toll will be the same as it is now. What you have calculated is the average delta V and so your
calculations are saying that if we have the average delta V that we do have then we will have the
death toll that we do have. You have, in effect, calculated the bleeding obvious.

Colin

 

[Colin Blackburn]

In article <[email protected]>, [email protected] says...

> Can someone *please* enlighten me? If I run into a house at 12 mph with my car the , presumably,
> the delta V is 12 mph?

Yes. But most crashes don't involve all the speed being lost in one bit, ie the driver brakes and
loses some speed and has a glancing blow which leaves the car moving. So for almost all crashes
delta V is less that V. The equation tries to relate the probability of death (of the driver) to the
delta V of the crash.

> No-one in the car (wearing seatbelts)would die under these circumstances from injuries sustained
> in such an impact.

No, there is a probability that you will die according to the equation kicking all this off.
However, that probability is small and at low speeds (ie where V is low rather than delta V) the
equation isn't tested.

Colin

 

[Paul Smith]

On Thu, 27 Feb 2003 09:06:50 -0000, "Just zis Guy, you know?" <[email protected]> wrote:

>Paul Smith wrote:
>
>>> The experimental uncertainites make the value effectively zero at speeds much below 30mph. I
>>> would be wary of concluding too much at 20mph, and disregard anything lower.
>
>> Yeah, that's a consideration. But would the message of the page change at all if 12mph was
>> altered to 20mph? And even if it did seem to alter a fraction, there's a list of unincluded
>> factors to pull it back.
>
>Unincluded factors?

But there's more...

This bit:

"What if we start talking about near misses? Perhaps we could say that
7.5 million accidents and near misses resulted in 1,164 fatals and push the average impact speed
down lower?

What if we start talking about excluding reckless drivers, joyriders, police drivers and drunks (any
that wouldn't be affected by the 12 mph speed limit)? Then we could reduce the 1,164 fatals perhaps
to 1,000 or less.

What if we exclude all those fatals where the driver crashed at above 50 mph impact speed? They
weight the average massively against the rest of us don't they?"

And those three are just a quick sketch. I think I've got about 4 or 5 more in some notes somewhere.
Suicides was one on the list.

>No, the message wouldn't change by changing the speed to 20mph - it would still be wrong The
>research on which you base the page simply does not apply to low-speed crashes, or to average
>driving speeds (it's crash impact speeds).

>And you've excluded the groups most affected by speed on urban roads - vulnerable road users. Only
>5 percent of pedestrians die when struck by a vehicle travelling at 20 mph, the proportion of
>fatalities rises to 45 percent at 30 mph and to 85 percent at 40 mph. The Joksch equation clearly
>doesn't apply to pedestrians. So even if drivers did modify their behaviour to exclude braking,
>thus enabling them to still /have/ crashes with the low limits you discuss, anything up to half
>the pedestrian fatalities would be prevented, even before the pedestrians started outrunning the
>12mph cars.

Pedestrians are in much the same boat though aren't they?

http://www.safespeed.org.uk/killspeed.html and http://www.safespeed.org.uk/proof.html

The first of those two pages has got in a little bit of a mess due to too many extensions, and is
due a re-write. But the facts are there OK.

>The whole 12mph page is ludicrous and you really should pull it.

I get more trouble and grief about this page than anything else, and that might be a reason to pull
it. As things stand, I'm hoping Joksch will reply and I'll consider a complete re-write. I don't
really want to change it much before he gets to reply, especially if he's "working on it".

The vital vital thing to come out of it is that there's a 1500:1 ratio of crashes to fatals (car
drivers) and yet everyone agrees that a 60mph delta V has around a 50% probability of death. The
discrepancy is mind boggling, and I'm determined to highlight it.
--
Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
cameras cost lives

 

[Paul Smith]

On Thu, 27 Feb 2003 07:13:49 -0000, "Michael MacClancy" <[email protected]> wrote:

>Paul Smith wrote:
>> The main point of the page is to highlight the difference between delta Vs and Vs.
>
>No it's not. The main point of the page is summarised by your words below.

>"It isn't speed that kills. We can reduce the speed limits endlessly or enforce them perfectly
>without ever hoping to get close to the thresholds where free travelling speed will play a larger
>part in the outcome than driver based factors like skill, attention, attitude and training level.
>In fact, small variations in these factors will have far more effect on accident rates and outcomes
>than big variations in limited or enforced speed. See elsewhere on this web site."

You picked the closing paragraph which is intended to put the conclusions in a wider context.

This is the paragraph that is intended to sum up the page.

"Since 12 mph bears no relation to any free travelling speed used on UK roads "something" must
intervene between free travelling and the actual crash. This "something" is of course driver
response. No one wants to crash. Most drivers, most of the time have effective strategies for
avoiding crashes. In practise the failures of these crash avoiding strategies are not normally
massive blunders resulting in impacts at free travelling speeds. Instead they are subtle
misjudgements followed avoiding actions leading to mostly minor crashes. The ratio of minor crashes
to fatal accidents is probably greater than 1,500:1."
--
Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
cameras cost lives

 

[Colin Blackburn]

In article <[email protected]>,
[email protected] says...
> On Thu, 27 Feb 2003 09:06:50 -0000, "Just zis Guy, you know?" <[email protected]> wrote:
>
> >Unincluded factors?
>
> But there's more...
>
> This bit:
>
> "What if we start talking about near misses? Perhaps we could say that
> 7.5 million accidents and near misses resulted in 1,164 fatals and push the average impact speed
> down lower?

How can a near miss be included? Since it doesn't have an effective delta V it is irrelevant in
calculating the probability. There is only a delta V if there is a collision between the vehicle and
some other object.

Colin

 

[Paul Smith]

On Thu, 27 Feb 2003 11:46:46 +0000, <[email protected]> wrote:

>On Wed, 26 Feb 2003, Paul Smith wrote:
>
>> >>> Face it, if the maximum is 12mph, the average is going to be less than 12mph and the delta V
>> >>> much less than 12 mph - 6 say? What does that do to your conclusions?
>> >>
>> >> Nothing. It says "we COULD kill just as many" not "we WOULD kill just as many".
>> >
>> >The right answer is, "we wouldn't kill as many".
>>
>> No it bloody isn't.
>>
>> "We could kill as many" is true.
>
>We are highly unlikely to, though. Not many people are killed in traffic jams. Claiming that we
>could kill just as many people at 12 m.p.h. as, say, 60 m.p.h., _may_ be technically correct, but
>it is very misleading.

Personally I find it enlightening. I honestly believe that we could reduce speed limits endlessly,
enforce them perfectly and save no lives.

In fact too much enforcement is implicated in a rise in the underlying fatality rate.
--
Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
cameras cost lives

 

[Paul Smith]

On Thu, 27 Feb 2003 11:58:25 -0000, Colin Blackburn <[email protected]> wrote:

>> >Unincluded factors?

>> But there's more...

>> This bit:

>> "What if we start talking about near misses? Perhaps we could say that
>> 7.5 million accidents and near misses resulted in 1,164 fatals and push the average impact speed
>> down lower?

>How can a near miss be included? Since it doesn't have an effective delta V it is irrelevant in
>calculating the probability. There is only a delta V if there is a collision between the vehicle
>and some other object.

Every near miss, incident and is a safety system failure.

The ratio of safety system failures to fatals is illuminating because every one is a
potential fatal.
--
Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
cameras cost lives

 

[Michael Macclan]

Paul Smith wrote:
> On Thu, 27 Feb 2003 07:13:49 -0000, "Michael MacClancy" <[email protected]> wrote:
>
>> Paul Smith wrote:
>>> The main point of the page is to highlight the difference between delta Vs and Vs.
>>
>> No it's not. The main point of the page is summarised by your words below.
>
>> "It isn't speed that kills. We can reduce the speed limits endlessly or enforce them perfectly
>> without ever hoping to get close to the thresholds where free travelling speed will play a larger
>> part in the outcome than driver based factors like skill, attention, attitude and training level.
>> In fact, small variations in these factors will have far more effect on accident rates and
>> outcomes than big variations in limited or enforced speed. See elsewhere on this web site."
>
> You picked the closing paragraph which is intended to put the conclusions in a wider context.
>
> This is the paragraph that is intended to sum up the page.
>
> "Since 12 mph bears no relation to any free travelling speed used on UK roads "something" must
> intervene between free travelling and the actual crash. This "something" is of course driver
> response. No one wants to crash. Most drivers, most of the time have effective strategies for
> avoiding crashes. In practise the failures of these crash avoiding strategies are not normally
> massive blunders resulting in impacts at free travelling speeds. Instead they are subtle
> misjudgements followed avoiding actions leading to mostly minor crashes. The ratio of minor
> crashes to fatal accidents is probably greater than 1,500:1."

Most people put their conclusions at the end. The section you say summarises the whole page doesn't
even refer to delta V. I conclude that the page is a load of tosh.
--
Michael MacClancy

 

[Colin Blackburn]

In article <[email protected]>,
[email protected] says...
> On Thu, 27 Feb 2003 11:58:25 -0000, Colin Blackburn <[email protected]> wrote:

> >How can a near miss be included? Since it doesn't have an effective delta V it is irrelevant in
> >calculating the probability. There is only a delta V if there is a collision between the vehicle
> >and some other object.
>
> Every near miss, incident and is a safety system failure.

Yes.

> The ratio of safety system failures to fatals is illuminating because every one is a
> potential fatal.

Yes.

But, you are suggesting using them in a relationship for which they are entirely inapplicable in
order to produce an even more startling, yet startlingly inapplicable, number. There is no delta V
in any near miss so they cannot be used in the relationship. The relationship was derived from
collisions, ie where there is a delta V. Is it any wonder your statistics are so open to ridicule
when you will happily misuse mathematics in this way?

Colin

 

[Colin Blackburn]

In article <[email protected]>,
[email protected] says...

> Personally I find it enlightening. I honestly believe that we could reduce speed limits endlessly,
> enforce them perfectly and save no lives.

That is a patently incorrect belief. If you had not used the word 'endlessly' and perhaps used 'to
much lower levels then they now are' it would at least have had a logical consistency but as it
stands it is laughably incorrect.

Colin

 

[Paul Smith]

On Thu, 27 Feb 2003 12:22:51 -0000, Colin Blackburn <[email protected]> wrote:

>> Personally I find it enlightening. I honestly believe that we could reduce speed limits
>> endlessly, enforce them perfectly and save no lives.

>That is a patently incorrect belief. If you had not used the word 'endlessly' and perhaps used 'to
>much lower levels then they now are' it would at least have had a logical consistency but as it
>stands it is laughably incorrect.

OK. I shouldn't have used the word endlessly. Big deal.
--
Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
cameras cost lives

 

[Alan Braggins]

Paul Smith <[email protected]> writes:
> On Thu, 27 Feb 2003 11:46:46 +0000, <[email protected]> wrote:
> >> >The right answer is, "we wouldn't kill as many".
> >>
> >> No it bloody isn't.
> >>
> >> "We could kill as many" is true.
> >
> >We are highly unlikely to, though. Not many people are killed in traffic jams. Claiming that we
> >could kill just as many people at 12 m.p.h. as, say, 60 m.p.h., _may_ be technically correct, but
> >it is very misleading.
>
> Personally I find it enlightening. I honestly believe that we could reduce speed limits endlessly,
> enforce them perfectly and save no lives.

Of course we could - we could issue the police with machine guns and order them to put the fatality
rate back up to what it was. But short of that, the death rate will fall, and that that is
_technically_ possible to bring it back up doesn't make it any more relevent to the real world than
your calculations.

 

[Michael Macclan]

Paul Smith wrote:
> On Thu, 27 Feb 2003 12:22:51 -0000, Colin Blackburn <[email protected]> wrote:
>
>>> Personally I find it enlightening. I honestly believe that we could reduce speed limits
>>> endlessly, enforce them perfectly and save no lives.
>
>> That is a patently incorrect belief. If you had not used the word 'endlessly' and perhaps used
>> 'to much lower levels then they now are' it would at least have had a logical consistency but as
>> it stands it is laughably incorrect.
>
> OK. I shouldn't have used the word endlessly. Big deal.

You sound like a kid in playground who's been proved to be stupid by the others.

It is a big deal. Using the word 'endlessly' creates an entirely different impression. It makes you
sound even more stupid than you obviously are.
--
Michael MacClancy

 

[Paul Smith]

On Thu, 27 Feb 2003 12:20:21 -0000, Colin Blackburn <[email protected]> wrote:

>> >How can a near miss be included? Since it doesn't have an effective delta V it is irrelevant in
>> >calculating the probability. There is only a delta V if there is a collision between the vehicle
>> >and some other object.

>> Every near miss, incident and is a safety system failure.

>Yes.

>> The ratio of safety system failures to fatals is illuminating because every one is a
>> potential fatal.

>Yes.

>But, you are suggesting using them in a relationship for which they are entirely inapplicable in
>order to produce an even more startling, yet startlingly inapplicable, number. There is no delta V
>in any near miss so they cannot be used in the relationship. The relationship was derived from
>collisions, ie where there is a delta V. Is it any wonder your statistics are so open to ridicule
>when you will happily misuse mathematics in this way?

Ah, I get it. You're worried because the delta V is zero. What if it's .01? 0.1? 1.0? 10?

Actually a delta V of zero is perfectly logical and OK. It's a true and useful description of a
non-collision incident.
--
Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
cameras cost lives

 

[Brian]

[email protected] (Robert McDonald) wrote in
news:[email protected]:

>> The point that crash energy equivalent to 12 mph crashes is all that's needed to kill the number
>> we DO kill, speaks volumes about the importance of speed in fatal accidents.
>
> Can someone *please* enlighten me? If I run into a house at 12 mph with my car the , presumably,
> the delta V is 12 mph? No-one in the car (wearing seatbelts)would die under these circumstances
> from injuries sustained in such an impact.
>
> Anyway, it's completely wrong to speak of 'energy equivalents' at a specific velocity without any
> mention of mass.
>
> BigRab

One other thing, imagine driving into a big block of jelly at 12 mph. Your car will decelerate to a
standstill, but would take significantly longer to come to a halt than a car driving into a 1000
tonne steel block.

Surely it is the delta V / delta t which is important? :-/

--
Brian

 

[Paul Smith]

On 27 Feb 2003 13:18:25 +0000, Alan Braggins <[email protected]> wrote:

>> Personally I find it enlightening. I honestly believe that we could reduce speed limits
>> endlessly, enforce them perfectly and save no lives.

>Of course we could - we could issue the police with machine guns and order them to put the fatality
>rate back up to what it was. But short of that, the death rate will fall, and that that is
>_technically_ possible to bring it back up doesn't make it any more relevent to the real world than
>your calculations.

It's not intended to be a trick statement. As Colin pointed out it really shouldn't use the word
"endlessly".

But we have been enforcing speed limits more than ever before. We have reduced speed limits more
than at any time since the 60s. And where are the casualty improvements? All the main national
figures demonstrate a accelerating loss of improvement trend. Some are already on the way up, and
there's worse to come in the 2002 figures.

See: http://www.safespeed.org.uk/stats/graphs.html
--
Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
cameras cost lives

 

[Paul Smith]

On 27 Feb 2003 13:32:12 GMT, Brian <[email protected]> wrote:

>One other thing, imagine driving into a big block of jelly at 12 mph. Your car will decelerate to a
>standstill, but would take significantly longer to come to a halt than a car driving into a 1000
>tonne steel block.

Or even just braking gently to a standstill. Same delta V.

>Surely it is the delta V / delta t which is important? :-/

There's obviously an assumption about the behaviour of real objects in real collisions. This is
going to be one of the main reasons that the Joksch equation is described as a "rule of thumb".
--
Paul Smith Scotland, UK http://www.safespeed.org.uk please remove "XYZ" to reply by email speed
cameras cost lives