20 mph zones are bad ...

[StuartG]

Or not? CC may not the only place where road casualty stats are bent to feed agendas. Listen from 13:40 on iPlayer

Speculating - did the Sun:

1) Employ such a clueless string of reporters, sub-editors and editors that they could publish such rubbish without checking?

2) Knew it was rubbish but it was such a good story published it anyway

3) Published because it fed the Murdoch agenda of making money by pleasing some of its major supporters and advertisers (aka the motoring lobby)

4) Or ...

Strangely I haven't had the Sun 'facts' quoted back to me yet. Or does that say something about the reading habits of my friends and colleagues?

 

[snorri]

Edit
A mischievous abuse of stats.

 

[StuartG]

? Is there a link Stuart?

Yes there is (from 13:40): http://www.bbc.co.uk/radio/player/b01lv7yn
The BMJ report referred to by the Bristol people is here:
http://www.bmj.com/content/339/bmj.b4469.full

 

[PK99]

3) Published because it fed the Murdoch agenda of making money by pleasing some of its major supporters and advertisers (aka the motoring lobby)

4) Or ...

?

Typical misunderstanding of numbers by functionally innumerate journalist?

Similar to a local councillor at a road calming meeting i attended, he claimed a 33% reduction in casualties in road calmed areas of the Borough. a question elicited the data: in the street in question RTA injuries fell from 3 to 2 pa in the test period. He was genuinely perplexed by the mixture of stunned silence and muffled sniggering that resulted.

 

[davefb]

amazing program.
just listening to the info about the carli index!!

 

[StuartG]

Typical misunderstanding of numbers by functionally innumerate journalist?

The Sun wouldn't dream of running a story about the law without also running it passed a lawyer. They wouldn't dream of running a story about statistics with running it passed a statistician? Oh yes they (and indeed the BBC) would. But to give credit to the BBC they did realise there was a problem and launched this (you're right davefb) amazing programme.

Even more amazing is how successful it has been received by the Radio 4 audience. Which really shows there is a thirst for programmes that try and be objective. Its also nice that Tim Hanford from an academic standpoint can get away with saying things about Government Minister's claims that, perhaps, a political correspondent both can't and daren't!

The More Than Less on cycle helmets was also brilliant but sadly not on iPlayer anymore. (The answer was we don't know the answer ...)

Meanwhile back in the sub-20 mph world hopefully the Bristolians will within a couple of years substantiate or otherwise the London study and we can get seriously into them or not whatever the Sun thinks. That's if that rag hasn't been lawyered out of existence ...

 

[davefb]

I was disapointed that the bbc ran the same 20mph story... But not surprised, even the grauniad with it's one time contributer dr ben goldacre publishes utter rubbish stories stat wise.

 

[Drago]

I heard the radio 4 programme, and it was a good listen. The big question seems to have been overlooked though - how many deaths in thes '20' zones were caused by drivers exceeding that limit?

 

[StuartG]

how many deaths in thes '20' zones were caused by drivers exceeding that limit?

What we do know is the average speed of all drivers appears to have dropped from 27 mph to 17 mph. Given that the method of restraint was passive calming and not penalty enforcement then the impact is to the square (or so) to the speed. In other words the fastest drivers may have reduced speed most. Its hard to imagine that reduction could have occurred without virtually eliminating travel of over 30 mph.

The combination of having more time to see and respond to an upcoming collision the force of the impact (if any) reduces by more than the square. In other words the saving in lives is more likely to come from people who push or exceed the limit (unrestrained 30 mph - do we imagine they are doing 40+ to calmed roads where 25/30 mph is very, very uncomfortable).

 

[dawesome]

the human body is designed to withstand running into a tree at about 20mph tops. Anything above that speed and the likelihood of death increases dramatically:

The Hull results are robust:

Typically within Hull, 20 mph zones have achieved reductions[106] in injury accidents of:
— Total accidents -56 per cent
— Killed & seriously injured accidents -90 per cent
— Accidents involving child casualties -64 per cent
— All pedestrian accidents -54 per cent
— Child pedestrian accidents -74 per cent.

It is estimated that at the end of 1999, 390 injury accidents had been prevented within the 20 mph zones which had been previously installed. 122 of these would have involved injuries to children.

Plus, of course, there doesn't have to be an accident for speeding in residential roads to be selfish, anti-social and threatening. It's noisier, it intimidates vulnerable road users, it's more polluting. We want a civilised community, not one ruined by selfish boy racers using public roads as their own personal racetrack.

 

[StuartG]

The Hull results are robust:

Typically within Hull, 20 mph zones have achieved reductions[106] in injury accidents of:
— Total accidents -56 per cent
— Killed & seriously injured accidents -90 per cent
— Accidents involving child casualties -64 per cent
— All pedestrian accidents -54 per cent
— Child pedestrian accidents -74 per cent.

Which are in line with the London results which were in the 40/50% area. Quite astounding really and beats most other road safety ideas into the ground.

But one must be cautious. These are studies in areas which may have had an historical bad KSI rate (justifying their imposition) or likely to be so. It is unlikely they were drawn at random and so one must be careful to extrapolate that the effect would be similar in all roads. There is also the Hawthorne effect*. Any change causes an effect in itself which may revert to the norm in time. So early results may be misleading.

Nevertheless this is a cause for action, albeit experimental, and not a reason to do nothing. Twenty's Plenty is a great idea as long as folks are careful not to overstate the stats and create hostages for the future which The Sun et al will jump on with rather more justification then this time around.

* In the Hawthorne factory it was proposed to increase lighting to increase productivity. They did it and productivity increased. Then a mischievous experimenter reduced lighting. Productivity increased again! This is now interpreted as the subjects improving their work because they were being paid attention to and what changed was supposed to help. So it wasn't the actual level of light that was important but the change. That's a very simplified version but the bottom line is if you remove the 20 mph limit and passive restraints - does the KSI rate revert or not?

 

[Boris Bajic]

the human body is designed to withstand running into a tree at about 20mph tops. Anything above that speed and the likelihood of death increases dramatically:

(Edited)

As a personal friend and lifelong (if occasional) dining partner of Our Lord God the Creator, I'd like to say that He (God) assures me he was working to no specific design remit or pre-determined impact-resistance criteria when he came up with the outline concept for humankind.

As far as I recall (we were three bottles of Merlot into a long dinner at the time) his essential notion was to build something pretty much in his own image, but without all the 'omniscient' bells and whistles. I gather the whole design brief is covered in a book, but it is not one I've read: Authors were Matt, Mark, Luke, John and others. A good read, I've been told.

He (God) was adamant when we spoke that at no stage did he carry out any work or write any design briefs on the basis of survivable speed of impact with any wooden flora (the design of which was also his work).

I think that statements like Dawesome's about the supposed design parameters of humankind do nothing to enhance the image of a very hard-working deity who has recently been getting some pretty rum press. He did not take into account anything to do with running at speed into trees when he put the blueprints up for consideration.

Can we please be careful about making wild, troll-like generalisations about what speed of impact the human body was or was not designed to withstand.

Apparently there was some rudimentary impact-resistance work done on early mouse prototypes, but this work came to nothing.

With God as my witness (quite literally) I cannot have made this up.

Thank you.

 

[dawesome]

[QUOTE 1994358, member: 45"]I wondered whether anyone would bring this up.

Did The Sun ask Safespeeding for a quote?[/quote]

Yep,they're exploiting the grief of poor old confused Claire, the late lamented Paul Smith's partner. She serves as a kind of Denise Bulger, exploited by a callous media.

Claire Armstrong of Safe Speed called for a halt to lower zones.
She said: “A 20mph limit does not make the road safer. Thirty is absolutely adequate.”

Poor woman,possibly mentally unstable from her mourning. Spouting dangerous nonsense she doesn't really understand.

 

[dawesome]

Which are in line with the London results which were in the 40/50% area. Quite astounding really and beats most other road safety ideas into the ground.

BMJ:

Setting London.
Main outcome measures All casualties from road collisions; those killed and seriously injured (KSI).
Results The introduction of 20 mph zones was associated with a 41.9% (95% confidence interval 36.0% to 47.8%) reduction in road casualties, after adjustment for underlying time trends. The percentage reduction was greatest in younger children and greater for the category of killed or seriously injured casualties than for minor injuries. There was no evidence of casualty migration to areas adjacent to 20 mph zones, where casualties also fell slightly by an average of 8.0% (4.4% to 11.5%).

http://www.bmj.com/content/339/bmj.b4469.full

 

[marinyork]

What we do know is the average speed of all drivers appears to have dropped from 27 mph to 17 mph. Given that the method of restraint was passive calming and not penalty enforcement then the impact is to the square (or so) to the speed. In other words the fastest drivers may have reduced speed most. Its hard to imagine that reduction could have occurred without virtually eliminating travel of over 30 mph.

The combination of having more time to see and respond to an upcoming collision the force of the impact (if any) reduces by more than the square. In other words the saving in lives is more likely to come from people who push or exceed the limit (unrestrained 30 mph - do we imagine they are doing 40+ to calmed roads where 25/30 mph is very, very uncomfortable).

I'd like to point out that the ideas for 20's plenty (and other schemes) isn't just based on road accident statistics.

It was theorised for a very long time that the impact mechanics of child vs car road collisions were particularly sensitive in the 17-35mph region. When this has been performed on crash testing you can see exactly why this is the case. It's only some recent cars with higher marks on the new crash tests that have performed adequately.