Research suggests that using quieter streets with less traffic exposes city cyclists to lower levels of air pollution than using more congested routes, although wind-speed has a significant influence on levels of pollution exposure experienced each day.
"A travel mode shift to active transportation such as bicycling would help reduce traffic volume and related air pollution emissions as well as promote increased physical activity level," explain Sarah Jarjour (University of California, Berkeley, USA) and colleagues.
"Cyclists, however, are at risk for exposure to vehicle-related air pollutants due to their proximity to vehicle traffic and elevated respiratory rates."
Over the past decade the city of Berkeley in California has developed a bicycle boulevard system involving installation of new road markings and signage on a series of quieter residential streets.
Jarjour and team recruited 15 healthy volunteers (11 men) aged 32.2 years on average to take part in a study assessing pollution exposure on the cycle boulevards versus more congested traffic heavy streets in the same city.
As reported in Environmental Health, the researchers fitted a global positioning system (GPS) and pollution monitors on the bike of each volunteer. The cyclists completed a low- and a high-traffic route (10 and nine times, respectively) in pairs between 8:00 and 10:00 am on weekday mornings during 19 days in April-June 2011. Lung function was tested using spirometry before, immediately after, and 4 hours after riding each route.
Jarjour and co-authors found that cyclists were exposed to significantly higher levels of ultrafine and fine particulate matter (UFPM and particles smaller than 2.5 micrometers [PM2.5]), carbon monoxide (CO), and black carbon (BC) on the high-traffic compared with the low-traffic route.
More specifically, the mean UFPM exposures were 14,311 versus 18,545 per cm3 in the low- versus the high-traffic exposure groups, and mean PM2.5 exposure was 4.88 versus 5.12 µg/m3, CO exposure 0.79 versus 0.90 ppm, and BC exposure 1.76 versus 2.06 µg/m3.
Notably, no changes in lung function were observed in the volunteers before and after cycling both routes, but Jarjour and team say that "this is not surprising given that our subjects were healthy and screened to not have asthma."
Weather conditions, particularly wind speed, had a significant effect on average daily pollution measures. Another factor influencing pollution exposure was time of day, and the researchers comment that "avoiding rush-hour periods significantly reduces cyclists' pollution exposure."
The authors concede that "more research in this field is still needed to more conclusively determine the long-term health effects of bicycle commuting in variable traffic conditions."
However, they conclude: "Our results indicate that choosing low traffic routes can decrease the exposure of bicyclists to air pollutants, potentially reducing associated detrimental health effects."
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