BORIS JOHNSON, London’s flamboyant mayor, has long been known for his cycling—continuing on his bike in defiance of traffic, other cyclists and tabloid photographers (pictured, right). But despite his best efforts, cycling in London remains a minority pursuit. Even after a decade of growth, still just 2.5% of people in London bike to work, according to the 2011 census. This, Mr Johnson thinks, is not good enough: “Our streets should be as famous for cycling”, he says, “and as popular with cyclists as the streets of Copenhagen or Amsterdam”. But why does cycling thrive in some cities and not others? Mr Johnson’s ambition will not be easy to live up to: in Amsterdam, 57% of the residents use a bike on a daily basis, accounting for 38% of traffic in the city. In Copenhagen, 52% of people cycle to their work, school or university each day. But even Britain has some extremely cycle-successful areas. In Cambridge, 30% of people commute to work by bicycle; in Hackney, a borough in east London, around 15% of people do. Troublingly for Boris, however, how many people cycle seems to be a function of what sort of people live in an area, more than anything else. In Britain, since cyclists tend to be affluent young men, having lots of them seems to be the key. Cambridge is a wealthy university town full of students; Hackney is the choice London borough for hip young web designers and graphic artists. So it is unsurprising that both have lots of cyclists. That also applies to Portland, Oregon, perhaps America’s most successful cycling city. In Amsterdam and Copenhagen, by contrast, most cyclists are women, while people of all ages and incomes use bikes.

So the question isn’t so much how to get people to cycle as how to get people who wouldn’t ordinarily cycle—such as women and old people—onto bikes. The first answer seems to be safety. In the Netherlands and Denmark, not only is the infrastructure good, the sheer number of cyclists means that there is relative safety in numbers. And in accidents the law favours cyclists in almost all circumstances, which probably keeps motorists on their toes. In Britain, two thirds of women say that the roads are too unsafe to cycle on. Safer roads would encourage more people to cycle. But safety isn’t everything. Milton Keynes and Stevenage, two British new towns, both have extremely good, segregated cycle paths—known as greenways—which separate cyclists and pedestrians from the roads. And in both towns, few people cycle: they prefer to drive on the fast segregated highways. To get people to cycle, you need to make them feel safe, but you also need to make other forms of transport slower and less comfortable. Indeed Hackney probably has more cyclists than other inner-London boroughs partly because its transport links are relatively worse than elsewhere in the city: it has no dedicated Tube line serving it.

Sadly then, Mr Johnson’s best hope for his cycle revolution may be that the sheer cost and inconvenience of other forms of transport in London push more people onto their bikes. Over time, that can create a culture of cycling: you are far more likely to consider taking a biking to work if one of your colleagues or friends already does. In Amsterdam and Copenhagen, that culture was never lost, even when cars became cheap after the second world war, perhaps because of the heavy congestion and narrow streets those cities have. In ever-more choked London, soon to reach a population of nearly 10m people, it may well take off again.