Fionnuala castigates me:
It’s the old “skiing makes you wealthy” phenomenon again. It’s not NECESSARILY that the more cyclists are on the road, the safer it becomes. The more intuitive and obvious explanation is that the safer it is, the higher percentage of people who will cycle.
So rather than saying that Copenhagen is safe to cycle because so many people per head of population choose to do so (thereby changing driver behaviour), we could say that huge numbers of people choose to do so because there are safe, wide, separate cycle lanes separated from both pedestrians and traffic by raised curbs.
Of course there’s also the element of high cyclist-demand leading to better safety facilities. That’s quite different to hoping that sheer numbers of cyclists on the roads will lead to more careful driving by would-be cyclist-killers.
She’s right, of course - correlation does indeed not prove causation. And I’m sure it’s true that safer cycling facilities persuade more people to cycle. I was going to write a longer post talking about how there was probably causation in both directions and measures to boost cycling could set off a virtuous circle of increased cycling -> safer cycling -> increased cycling, but decided not to bore you with all the details. Well, never again.
Fionnuala says it’s more intuitively obvious that “the safer it is, the higher percentage of people who will cycle”. Sure, but I can think of good reasons why more cyclists on the road may change driver behaviour. At the most basic level, larger groups of cyclists make each individual cyclist more visible. With more cyclists around, drivers become more aware of how cyclists behave and better able to predict their movements (see the ‘Shared Space‘ concept, based on the idea that the more visible pedestrians are the more carefully drivers drive). More cyclists on the street can also mean that car drivers are obliged to actually respect facilities for cyclists such as green boxes, staying safely behind a group rather than crowding dangerously around an individual. And drivers in areas where cycling is common are more likely to know cyclists personally or be occasional cyclists themselves, which should create a less oppositional climate than one in which cyclists are mostly younger men.
There’s also better evidence around than the simple cross-national averages I posted about. In “Safety in numbers: more walkers and bicyclists, safer walking and bicycling” P.L. Jacobsen cites two interesting studies comparing accident rates at individual junctions in the same city:
Research at specific sites has shown that collisions between a motorist and a person walking or bicycling diminish where more people walk and bicycle. Ekman examined numbers of pedestrians, bicyclists, and motorists, and serious conflicts among them at 95 intersections in Malmö, Sweden. He found that after adjusting for the number of bicyclists, the number of conflicts/bicyclist was twice as great at locations with few bicyclists compared with locations with more. In fact, the number of conflicts/bicyclist decreased abruptly with more than 50 bicyclists/hour. With pedestrians, Ekman found that although the number of conflicts/pedestrian was largely unaffected by numbers of pedestrians, the conflict rate was still affected by numbers of motorists.
Leden also reported a non-linear relationship in two examinations of intersections. In a before and after study, he examined changes in numbers of bicyclists and collisions between motorists and bicyclists in response to changes in physical configuration at 45 non-signalized intersections between bicycle paths and roadways in Gothenburg, Sweden. The total number of collisions increased with the 0.4 power of the increasing use of the intersections by bicyclists. He also examined police reported injuries to people walking at approximately 300 signalized intersections in Hamilton, Ontario, Canada. The number of collisions increased with the 0.32 to 0.67 power with increasing numbers of pedestrians.
I find this pretty persuasive, because (a) cycling facilities are unlikely to vary as much within a city as between countries, (b) the incidence of cycling at a particular intersection relative to others in the same town is to some extent a given based on its location and independent of its characteristics - in other words, it seems unlikely to me that quiet intersections will suddenly become busy ones just because they are made safer.
All of which is not to say that intervening to make cycling safer isn’t a good idea. It’s a very good idea, especially because it can give a big boost to the kind of chain reaction that appears to have taken hold in Denmark and the Netherlands.