Friday, 4 September 2009

Danger in numbers

Earlier this year the Cyclists Touring Club issued a much-publicised report which basically argued that people have an exaggerated perception of the risks of cycling, and that cycling is a safe transport mode, which gets even safer the more people there are who cycle:

London has seen a 91% increase in cycling since 2000 and a 33% fall in cycle casualties since 1994-98. This means that cycling in the capital is 2.9 times safer than it was previously.

At the time I suggested this was very questionable.

There is a very basic flaw in the CTC’s statistical analysis, because what it identifies as London’s ‘91% increase in cycling’ is no such thing. That figure derives from Transport for London’s measurement of cycling on just 40 main roads, which is NOT ‘cycling in London’. London consists of 32 boroughs plus the City of London, and the London Borough of Waltham Forest alone has some 1,300-1,400 roads. TfL’s statistical methodology remains opaque (when and how often are the measurements taken?) Comparing cycling injury statistics for Greater London as a whole with cycle use of just 40 main roads is classic bad science.

Personally, I think London is a dangerous city to cycle in, where personal safety cannot be measured by injury/fatality statistics but by exposure to risk. I believe that risk can most effectively be reduced by road traffic law enforcement (currently minimalist), by an overhaul of judicial attitudes to the criminally negligent use of a motor vehicle (at present dangerous, risk-taking drivers are treated with extreme indulgence) and by engineering roads to prioritise cycling.

More cyclists in London may simply result in more injured and dead cyclists. This is suggested by some new research released today, although its statistical basis is not meaningfully identified and I don't much like the language of its presentation and media reception.

Professor Ayton said: "People dread situations where many people may be harmed or killed at once, and so will avoid these situations. Instead, we'll choose less dreaded but sometimes actually riskier alternatives in which the same or even a greater number of people are likely to be harmed or killed - but over a longer period of time."

Analyses of the data showed there was a significant decrease in tube travel and a corresponding increase in cycle travel around London following the 7th July attacks. When compared to the 10 year period prior to the attacks, the second half of 2005 also had significantly more cyclist casualties than would be expected - there were 214 more cyclist casualties in this period than would be predicted from historical trends.


Prof Peter Ayton, from City University, who led the study, said: “People avoided things in which large numbers of people were killed at one time and switched to what looked like more innocent methods of travel like bicycling.

“But if you asked which killed more people in the last 10 years in London, international terrorism, or bicycles, the answer would definitely be bicycles.

I think he means drivers.