The front page of the Times today is devoted to its new campaign to make cycling safe. It shows that the love affair with our bikes has just got serious. We want the speed, convenience and health benefits of a life on two wheels and, despite the dangers, we are willing to fight to make that relationship work.

The problem is that, even if we could convince the majority of people to see the upsides, the reality of our unfriendly roads stops them from taking the plunge. All the surveys show that fear is the biggest barrier to an increase in cycling. Indeed, many cycling campaigners may see the Times campaign as counterproductive, as it will reinforce those fears.

London's mayor, Boris Johnson, certainly takes this view and is bullish in his determination that cycling must be a wholly feelgood story. As a London assembly member, I have twice been lectured by the mayor about the need "as an honest politician" to tell the truth, that cycling is getting safer. I was happy to do so, as I had been spouting figures for years showing that it was twice as safe to cycle in London than it was in 1990s. Then I decided to check my facts and realised that the mayor can't say that cycling has been getting safer since he was elected. Something has gone wrong in London and no amount of feelgood publicity is going to cover up the images of ghost bikes and angry protests at dangerous junctions such as Kings Cross.

There is an irony to a cycling mayor becoming a big barrier to a cycling revolution, but that is what is happening. The key change that we need in London is to reinstate the road user hierarchy, which Johnson scrapped in his revised London Plan. This hierarchy made the disabled, pedestrians and cyclists the priority when roads were being redesigned. Without reinstating this hierarchy, the engineers at Transport for London will consistently build roads that favour cars and lorries. This was the key problem at the Bow roundabout, where two cyclists died from left-turning lorries. Recommendations in one of TfL's own reports were ignored because, under Johnson, motorists' time is more important than cyclist and pedestrian safety.

Many of the other changes to our road network, in London and elsewhere, flow from this simple direction that vulnerable road users should come first. My assembly report, Braking Point, showed the big advantages of making 20mph the default speed limit for urban areas and, as the previous mayor's road safety ambassador, I pressed for the adoption of the zero-casualty approach applied in Scandinavian countries. Johnson needs to stop thinking about which roads he is happy to cycle on and instead design roads that either an eight-year-old or an 80-year-old would feel safe and happy to cycle on.

I believe that creating a critical mass of cyclists on our roads will in itself make them safer. I have also spent over a decade pushing for more cycle training, but we have to be clear that the mayor's advice to cyclists at a recent assembly meeting that you will be OK if "you keep your wits about you" is no excuse for inaction on building high-quality cycle lanes. We need to adopt the Dutch approach, which gives cyclists and pedestrians legal priority over cars in many urban areas. Sometimes we need segregated spaces, sometimes shared spaces, but real innovation in this country will come from simply filtering cyclists through traffic lights at dangerous junctions, or even changing the culture of our roads by ensuring that motor vehicles give way to cyclists and pedestrians at junctions.

Changes to the law on lorry design are well overdue and I welcome the growing consensus that mirrors and sensors need to be fitted as standard. We also have to escalate the work by the police on reforming the freight industry, and reaching the small-scale tipper truck operators who account for much of the carnage. Above all, the police have to get behind the idea of a cycling revolution and deal with the huge numbers of illegal drivers and hit-and-runs on our sometimes lawless roads.

I believe that cycling is the future for modern cities, but it will take bravery on the part of those in charge to liberate people from their cars by convincing them that conditions for cyclists have really changed. That will only happen when safety, rather than keeping cars moving, is our No 1 priority.