When I started cycling in London eight years ago I felt I was virtually the only one, battling for space with taxis and buses. It was a fight with few allies. Today, things are very different – I'm one of the pack surging away at the traffic lights. Official figures show more miles were travelled by bike in 2008 than for each year since 1992. Cycling has almost doubled on London's main roads in nine years and increased by 30-50% in cities such as Bristol, Leicester and Leeds.

But it's really remarkable that despite the increase in cycling, casualties suffered by cyclists are still down by around a third. To anyone who doesn't cycle this might seem a bit odd. Shouldn't more cyclists mean more crashes and injuries? As those who cycle will know, however, the more cyclists there are the safer it will be for everyone.

CTC (the UK's national cycling organisation) found that the same phenomenon occurs if you examine different areas within the UK. Cambridge, where a quarter of people cycle to work, or York where it is about one in eight, have a much lower risk of injury for cyclists than places where you hardly ever see a cyclist on the streets.

Why does this "safety in numbers" effect occur? The vast majority of cyclist injuries result from crashes with motor vehicles, and most of these appear to be primarily because the driver "looked but did not see". Cyclists (and motorcyclists) have even given this type of crash a name – Smidsy, an acronym for the drivers' refrain, "Sorry, mate, I didn't see you!"

These type of crashes start to decrease as cycling levels rise.

Take the hypothetical case of Bob the Driver, who last rode a bike when he was still in school uniform. Bob drives up to a junction with a major road, glances right and, not seeing anything car-shaped, pulls out into the path of the "unseen" cyclist. Crash and injury result. If, as Bob approached the junction, there was a stream of cyclists crossing in front of him, he probably won't make the same mistake.

As more people cycle, one of the new cyclists may be one of Bob's relatives or friends, or even Bob himself. When riding a bike he is less likely to pose a risk to others than when he is driving – and more likely to understand cyclists' needs.

Even though cycling gets less risky at the same time as more people taking up cycling, there may come a point where the overall number of injuries to cyclists actually increases. There are far more people killed cycling in the Netherlands than in the UK, for example, even though the population is smaller. But the Dutch cycle ten times further than here, and the risk per mile is substantially lower. After years of badgering, the government has finally agreed to present casualty data as risk per mile rather than numbers of injuries and deaths.

At a population level, of course, not-cycling is far more dangerous than cycling. The life expectancy of non-cyclists tends to be two years shorter, with 39% higher all-cause mortality than cyclists. But most people still associate cycling with danger. This is partly because this seems to be the main message of government and local authority advertising.

I'm often told I'm brave to ride a bike but few people consider it brave to get out into the garden and do a bit of weeding. Yet in reality this is a more dangerous activity than getting on two wheels. An hour spent gardening is more likely to result in injury than the same time spent cycling. So remember, next time you step outside to clip the hedge, beware of the risks you are running!

• Chris Peck is the CTC's policy coordinator. The CTC is a national cycling organisation.