Fatality risk on Boris-bikes?
I was very saddened by the death on Friday of a Boris-bike rider in Whitechapel High Street, particularly as I am a frequent and enthusiastic user of the scheme. But as a statistician, I also immediately wondered how surprised I should be about the fact that this was the first fatality of the bikes. My conclusion, using a very rapid and crude analysis, is that it does not suggest that Boris-bikes are of higher risk than average cycling, and if anything we have been fortunate that it has taken this long for the first fatality. Of course this does not lessen the tragedy of the event.
Transport for London report that between December 2010 and 31st May 2013 there were around 22,000,000 Barclays Cycle Hire (the official name) trips in London. There were 750,000 trips in May, so let’s assume that by July 7th there were around 23,000,000 trips. These journeys were an average of 20 minutes during the week and 28 minutes at the weekend, so conservatively we could assume 1.5 miles for each trip, giving a total of at least 34,000,000 miles cycled on Boris bikes since the opening of the scheme to non-members.
The Department of Transport reports that in 2011 there were 22 cyclist deaths per billion km (620,000,000 miles), which works out as one cycling fatality expected every 620,000,000/22 = 28,000,000 miles [see page 234 of this report, eventually found through the shambolic chaos of the government statistics web-links]. Of course Boris-bike users are not average: they are probably somewhat higher risk since in London and include inexperienced tourists, compensated by being lower risk by not being very old or young, and cycling extremely heavy and slow bikes. They also rarely wear cycle helmets, but I am not getting into that tricky area .
If we very crudely assume these factors cancel out and Boris bike trips are of average risk, then to have a fatal accident after 34,000,000 miles is, unfortunately, not surprising. In fact, very roughly, there is perhaps less than 30% chance that it would have taken this long.
So I am not very surprised to hear of this tragic accident, but do feel shocked that it happened on a so-called cycle ‘superhighway’. My personal opinion, as someone who has negotiated that particular stretch of road with some trepidation, is that far more needs to be done to make cycle-friendly and protective routes in London.