Cycling and air pollution

Air pollution has been in the news a lot recently with the release of the NICE draft guidelines on air (see www.camcycle.org.uk/jumpto/NICEdraftguidelines ). Air pollution is a growing problem in our cities, with an estimated 40,000 deaths a year in the UK attributed to it (see www.camcycle.org.uk/jumpto/rcpeverybreathwetake). So what are the risks to people cycling?

The path across Coe Fen, with nose to tail traffic on Trumpington Road beyond
Image as described adjacent

Health benefits of cycling outweigh harm due to air pollution

The first thing to bear in mind is that physical activity is a huge benefit to mental and physical well being. While exposure to air pollution is a danger to health, so is inactivity, and in all but the most polluted cities in the world, such as Delhi, the benefits of cycling outweigh the harm of air pollution (www.camcycle.org.uk/jumpto/benefitvsrisk). For the average global city, you would need to cycle 7 hours a day to start to negate the benefits: more than anyone is likely to do unless cycling is their job.

People inside vehicles are also exposed to air pollution

Exposure to air pollution happens whatever your mode of travel. Some studies have even found that the exposure to air pollution may be greater to car occupants (www.camcycle.org.uk/jumpto/airpollutioncardrivers).

Duration of exposure is also a factor: in Cambridge cycling is often the fastest mode of transport, and so overall duration of exposure can be lower compared to walking, taking a bus or driving along the same route. When before Christmas traffic was moving very slowly and parts of the city were grid-locked, people in cars had no option to remove themselves from exposure, while people cycling could often move past queues and make their journey is the same time as usual.

Routes away from main roads

In a real-world sample of air pollution exposure in London, cycling was least exposed to air pollution, and car occupants most exposed on a given journey (www.camcycle.org.uk/jumpto/healthiesttransportvideao). One reason cited for the low exposure was that cycling can avoid the most polluted main roads. Cambridge has many quiet and off-road routes which can reduce exposure to air pollution, though this is only one factor in choosing a route.

Effects of intensity of exercise

While some studies record passive exposure to air pollution, others try to model the effects of exercise on exposure. Elevated breathing can increase the rate of pollution exposure, but faster cycling can also reduce the overall time exposure. One model suggests the trade-off between these effects is optimal cycling at between 12kph and 20kph (www.camcycle.org.uk/jumpto/airpollutionandspeed), which would be similar to the typical Cambridge person on an upright bike cycling in normal clothing for transport. This study is based on a number of assumptions, and factors such as fitness, but also bike fit and maintenance, can have an effect: a poorly maintained bike can make you work harder to achieve the same speed!

General advice is based on assumptions about the health of people cycling. People with respiratory or heart issues should seek individual advice about exercise and air pollution.

Conclusion

We should all be concerned about air pollution. Air pollution doesn’t just affect us while we are travelling, but also in our homes and workplaces. However, the dangers aren’t necessarily greater to people cycling, and can be lower.

In the long term, reliance on pollution-emitting vehicles needs to be reduced or eliminated to improve the quality of the air in our cities. More people cycling is part of a suite of measures that can create this change. It would be short-sighted, and flying in the face of existing evidence, to curb cycling activity because of fears about air pollution.

Hester Wells