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Separating bikes from traffic can halve pollution exposure, study finds

Cycle routes away from motor traffic can halve pollution exposure, while parking protected cycle tracks can cut cyclists' pollution exposure by 20-30 per cent, according to recent study...

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 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 “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.

Cycle paths likely to decrease pollution, not worsen it

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.

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Twowheelsaregreat | 7 years ago

Is there a way I can test what damage commuting into work with the rush hour traffic and the fumes are doing to me? It is really bad and I don't commute within a city. I'm on the outskirts. I'd love to be able to measure the amount of pollution my body has consumed. It does make me feel ill somedays and it's the diesels that are worse. Horrid smell. I daren't breathe too deeply but it's awkward cycling at high tempo.

Additionally European and American cars have their exhausts on the near side whereas Japanese cars have their exhausts located on the off side for obvious reasons. I really think the government should offer bigger subsidies on physically small cars that have hybrid technology or small petrol engines and exhausts located on the off side.

We've really got to get rid of this culture where nearly everyone aspires to owning a large car. Small car due to their light weight will have less of a detrimental effect on infrastructure, they will pass cyclists with a wider gap due to more space for overtaking, less emmissions, less noise (debatable maybe) and more parking spaces as existing ones could be made smaller. We need to look to Japan and their policies within the auto industry for inspiration now. Although their cycling infrastructure's pretty poor.

horizontal dropout replied to Twowheelsaregreat | 7 years ago

Twowheelsaregreat wrote:

Is there a way I can test what damage commuting into work with the rush hour traffic and the fumes are doing to me?

You could try one of these: I'm not endorsing them, you can make up your own mind - I did have one but lost it the first day : -( . It was a bit heavy on phone battery if used with full tracking but you could turn that off and take a sample every now and then.


Simon E | 7 years ago

Could really taste the vehicle pollution on the roads in Shrewsbury today. I don't normally notice it but today it was awful. Am guessing it must be the cold weather.

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