Tag Archives: IAM

Repost: Exclusive: things tend to have a greater effect on the world once they exist

So the Institute of Advanced Motorists have press released the fact that casualties are up on 20mph streets (deaths are down, but they were already in single figures, so that’s random). I thought it might be worth reposting this sarcastic rubbish that I bashed out last time some idiot tried to claim that an increase in casualties on 20mph roads is evidence of their failure.

I heard on the lunchtime news on Radio 4 today the shocking news of an increase in the number of people injured on 20mph streets. Back when there were fewer 20mph streets, fewer people were injured on 20mph streets, they revealed. Now that there are more 20mph streets, more people are being injured on 20mph streets. This road safety intervention, they concluded, isn’t working.

This watertight logic perhaps also explains why BBC News have been so quiet on the destruction of the NHS. Before the NHS existed, literally nobody at all died in any of the then non-existent NHS hospitals. Almost as soon as the NHS was created, people started dying in the newly created NHS hospitals. Clearly the NHS doesn’t work.

Members of the Association of British Nutters will no doubt be getting very excited about these numbers, but before they make rash recommendations they should remember that back before the British motorway network was built, there were literally no people injured on the British motorway network, whereas now that the British motorway network exists, there are lots.

I hope that the main elements of the astonishing innumeracy that went into the BBC story — the failure to put the raw numbers into any kind of useful context, either of the rapid growth in the number of streets with 20mph limits as it has become easier to set the limit (or their changing nature as 20mph starts to roll out beyond quiet residential streets onto busier high streets), or of the far higher number (and, more importantly, rate) of injuries and death on either equivalent 30mph streets or on the same 20mph streets before the speed was lowered — should be obvious. Needless to say, reducing speeds on a street from 30mph to 20mph cuts injuries, regardless of the entirely banal fact that those few injuries which remain will thenceforth be added to the tally for 20mph streets instead of that for 30mph.

So, mockery over,  there’s a more important point: should an increase in injuries, if there really had been one, automatically kill off further roll out of 20mph zones?

Those who dwell at the bottom of Bristol’s Evening Post presumably think so

It beggars belief that the council intend reducing the 30mph speed limit. A limit introduced when there was no such thing as MoT’s, ABS brakes, crash zones on the front of cars and good street lighting.

I can see no justification in spending this money and would dearly love to know who Bristol City Council think it will benefit? It certainly won’t be the youth, disabled or elderly.

James R Sawyer clearly thinks that the 20 zones must be all about safety, as he argues that his ABS brakes and crash zones are already plenty enough to keep him safe as he drives through Bristol at 30. But Bristol have always been clearabout why they’re moving towards a 20mph city:

Councillor Jon Rogers, Cabinet Member for Care and Health, said: “…20 mph zones create cleaner, safer, friendlier neighbourhoods for cyclists and pedestrians. They are popular with residents, as slower traffic speeds mean children can play more safely and all residents can enjoy calmer environment.”

Slower speeds are not a simple issue of cutting crude injury statistics. They’re more about reviving communities which have been spoiled and severed by traffic speeding through them, reclaiming a little bit of the public realm that has been monopolised by the motorcar, and enabling liveable walkable neighbourhoods to thrive. Far from “certainly no benefit for the youth, disabled or elderly”, we know much — some of the research having in fact been carried out in Bristol itself — about the many adverse effects of higher speeds and volumes of traffic, and the loss of shops and services due to car-centric planning and living and the blight of high streets by arterial traffic, on the mobility of those most excluded from the car addicted society, particularly the young, the elderly, and the disabled. If they’re lucky, these people will be forced into dependency on those willing to help them get around; if they’re unlucky, they will simply be left isolated and severely disadvantaged. But of course, we don’t like to acknowledge the existence of the large numbers of people who are excluded from much of our society, culture and economy by our rebuilding the world with nobody in mind except car owners.

The injury statistics cited in the BBC News piece include minor injuries, which is most injuries at slow speeds — little things which don’t require a hospital stay. What are a few more cuts and bruises if it means that thousands of kids are free to walk to school with their friends instead of stuck inside mum’s car? Would we rather keep the infirm all shut up and sedentary with no access to the shops and the services they need, too intimidated by the anti-social behaviour of motorists to cross the road, than risk one person having a fall?

These strands can be tied together by the other piece of context that would have been worth including in the BBC piece: in the same year that injuries in 20mph zones increased, injuries to pedestrians and cyclists in general increased — in part because there are more to be injured. It has always been the case that the great road safety gains that successive governments have boasted of have been won mainly by making streets so dreadful that people find them too frightening, stressful, unpleasant, humiliating or ineffective to walk, cycle, or do anything other than sit in a secure metal box on. Start making the streets a little bit less awful and people return to them.

“The overall results show that ‘signs only’ 20mph has been accompanied by a small but important reduction in daytime vehicle speeds, an increase in walking and cycling counts, especially at weekends, a strengthening of public support for 20mph, maintenance of bus journey times and reliability, and no measurable impact on air quality or noise.”

Like cycle tracks, which people still like to claim increase car-cycle collisions (they don’t) despite before-and-after studies largely ignoring the fact that the point of cycle tracks is to widen bicycle use from the confident and quick witted to the people who were are otherwise too scared, stressed or infirm to do so, so invalidating the before-and-after study design, an increase in minor injuries after speed limit reduction, even if it were really to happen, would be far from proof of a failure.

Postscript, July 2014

The IAM make a thing of the DfT stats showing a 26% increase in serious injuries in 20mph limits and a 9% decrease in 30mph limits. Given that the base figures for the two sets are so different, that amounts to 87 more injuries in 20 zones and 1102 fewer injuries in 30 zones. Of course, the only figures that would really matter (in the absence of a double blind randomised controlled trial) are before/after comparisons of the streets that have switched and/or case-control studies of those streets (at least, for measuring injuries; as I said before, there are other important outcomes to 20 zones besides injury rates). And given that these numbers are not (and could not really be) normalised to the changes in total length of the two types of street, and are influenced by far too many confounding variables, I wouldn’t dream of suggesting that they’re worth drawing any conclusion from. But if you’re intent on drawing a conclusion, given the trend in switching 30mph streets to 20mph streets, a net reduction in serious injuries of 1015 seems like a far more pertinent one than a 26% increase in injuries on 20mph streets.

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