“CYCLISTS often don’t help themselves,” says a police community support officer, leaning on his yellow bicycle by the Bow roundabout in east London. He points at a man on a single-gear bike waiting at traffic lights, and explains how he has misread the signals and put himself in danger.

It has been a particularly brutal month for cyclists in the capital. On November 18th, a man in his 60s died in a crash with a lorry in Camberwell, south London—the sixth death in just two weeks. The Bow roundabout, where another cyclist died on November 13th, has become a symbol for many of what is wrong with cycling in London. They argue that infrastructure installed in the capital by Boris Johnson, its mayor (and a keen cyclist himself), is dangerous. Mr Johnson says that his cycle lanes are safe, and that some cyclists ought to be more careful—not wearing headphones, for example.

Taking a bike on to Britain’s roads is not as dangerous as it once was. Estimates from the Department for Transport show that, per million miles cycled, the number of cyclists killed or seriously injured has fallen by 33% since the 1990s (see chart). But the rate has recently moved up again, even as the number of road accidents in general has fallen sharply. In London, cyclists made up 22% of all casualties on the roads in 2012, up from just 10% in 2006. Across Britain, last year’s total of 118 deaths was the highest since 2007. A particular problem is with lorries. More than half of cycling deaths in London between 2008 and 2012 involved heavy goods vehicles. A ban on night deliveries means that most lorries enter the city in the morning, just when cyclists are commuting to work, says Danny Williams, a cycling blogger. Harriet Harman, the Labour Party’s deputy leader, has called for lorries to be banned from London in the rush hour as a way to reduce deaths. Badly designed infrastructure doesn’t help, says Christian Wolmar, a transport expert. A large majority of serious injuries happen at junctions and roundabouts, yet it is not easy for cyclists to avoid the most difficult spots. Parts of Mr Johnson’s “cycle superhighways” push unwitting cyclists into traffic, says Mr Wolmar. The Bow roundabout is typical: a separate green light is intended to direct cyclists to get ahead of the traffic, but it is easy to misunderstand the signals and cycle straight into the line of vehicles turning left. Poor planning often promotes dangerous behaviour by cyclists, says Rachel Aldred, of the University of Westminster. If the rules at a junction are not clear, they are easy to break. Novice cyclists are no more likely to suffer accidents than seasoned road warriors. Rather, they will only take to the road when it becomes safe. In other countries, such as Denmark, when the number of cyclists increased (as it has in Britain in recent years), the absolute number of injuries fell.

In Britain, most cyclists are still young men: two-thirds of women say the roads are too dangerous to cycle on. In London Mr Johnson is investing some £900m in new infrastructure improvements over a decade, including new segregated cycle lanes. He has taken some measures to improve the safety of heavy goods vehicles, insisting they install equipment to protect cyclists. Other British cities are now following his lead. Cycling will prosper only if cities manage to make it feel a lot safer than it does today.