Separating bikes from traffic can halve pollution exposure, study finds

Cycle tracks separated from motor traffic by as little as 7m can reduce cyclists’ exposure to air pollution by 20-30 per cent, while those further from roads can cut exposure to traffic fumes by up to half, according to a new study.

Researchers at the University of Canterbury, in New Zealand, measured cyclists’ exposure to fine particulate matter and carbon monoxide on the road, on the pavement, and on an off-road cycle path, and found exposure decreased 20-30 per cent on the pavement and 40-50 per cent away from traffic, compared to on the road.

Professor Simon Kingham, one of the authors of the report, Potential pollution exposure reductions from small-distance bicycle lane separations, told road.cc the findings suggest segregated cycle tracks can reduce cyclists’ exposure to motor vehicle pollution, especially on busy roads.

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In the experiment three cyclists rode in unison with identical monitoring equipment along a road, adjacent pavement (7m away), and an off-road path (19m away in a park) for six hours 45 minutes over five afternoons in Autumn, in the central city park area of Christchurch, New Zealand. They sampled concentrations of ultrafine particles (UFPs), carbon monoxide (CO) and fine particulate matter (PM10).

The study concluded: “Mean exposure to UFPs and CO were approximately 20–30% (po0.01) lower at the sidewalk and 40–50% lower at the path, than at the road (po0.01).

“These results highlight the potential exposure benefits of segregating cycleways, which helps inform city planning. Separating cycle lanes on key routes could help reduce cyclists' cumulative intake of pollutants, especially on heavily-trafficked roads.”

Even a small separation from traffic reduces pollution exposure

Professor Kingham, who is Director of the Geospatial Research Institute and Director of the Geohealth Laboratory at the University of Canterbury, told road.cc: “Even very small separation (pavement vs road; albeit largely with a row of parked cars between) sees a significant reduction in pollution.

“Just locating cyclists behind parked cars, or similar separation sees a significant reduction in pollution exposure.”

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While similar tests have been carried out before, using stationary monitors, this may not reflect exposure levels when moving with a stream of traffic.

An earlier study from 2013 by the University of Canterbury showed car drivers were consistently exposed to higher levels of carbon monoxide, while on-road cyclists were exposed to higher levels of pollutants than off-road cyclists. Car and bus occupants were exposed to higher levels of all pollutants than cyclists, even on the same stretch of road.

The recent study, published in the Journal of Transport & Health in October, quantifies that reduction in pollution exposure over a relatively small distance.

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​Kingham, whose research is broadly focused on researching the relationships between urban environment and health, dismissed recently-cited claims cycle infrastructure increases pollution.

“I’d be surprised if anyone can find any evidence that cycle paths increase traffic pollution by slowing traffic down. On the contrary the presence of cycle paths is likely to increase numbers of people cycling that reducing traffic volumes,” he said.

The study’s authors note levels of cycling in countries like the USA, Australia and New Zealand are 30 times lower than the Netherlands, at just one per cent of all trips, and a lack of safe infrastructure and “perceived and real risk of injury severely inhibits the growth of cycling uptake in these countries”.

It says high car ownership and incomes mean there is less demand for government investment in active travel and public transport which “highlights a need for strong scientific studies that demonstrate quantifiable benefits” to investment in active travel infrastructure, "thereby improving city liveability while decreasing traffic congestion and associated emissions.”

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Although cyclists are exposed to lower levels of pollution, the fact they are exercising, and therefore breathing more, affects exposure, says Kingham. “Cyclist are generally exposed to cleaner air than car drivers wherever they cycle although respiration may mean that dose could be the same, or higher, for cyclists.”

A previous study from Portland, Oregon, in the US, found moving a bike lane from the roadside to the inside of parked cars, a distance of 3.5m, reduced carbon monoxide exposure by 38 per cent for cyclists. However, a study in Auckland, New Zealand found once higher breathing rates, elevated by exercise, were accounted for, those cycling and walking would need to be 6-14m from traffic to equal drivers’ exposure to pollution.

According to Kings College, 90 per cent of the UK’s carbon monoxide emissions are from road transport, caused by incomplete, or inefficient combustion of fuel in cold or badly tuned engines. PM10, meanwhile, is a fine particulate emitted by, among other things, diesel engines.