Cyclists ride their bicycles during "No Car Day" in Bogota, February 5, 2015. Jose Gomez / Reuters

Bike lanes aren’t enough, according to a new Fort Collins commuting study.

We’ve known for years that cycling, for all its health benefits, has a dark side: Bikers inhale more black carbon than pedestrians do. Some studies have suggested that cyclists can reduce their exposure to air pollution by taking alternative routes. But a recent study of commuting in Fort Collins complicates that recommendation.

Researchers at Colorado State University followed 45 bicycle and car commuters in Fort Collins and measured their exposure to multiple hazardous air pollutants: black carbon, carbon monoxide, and particulate matter. Compared to drivers, cyclists tended to have higher mean exposure to particulate matter but lower mean exposure to carbon monoxide. They were also able to reduce their mean exposure to black carbon and carbon monoxide by using alternate routes (pictured in the figure below).

Map of Fort Collins showing the direct (black) and alternative (blue) routes taken by the study participants. (Journal of Exposure Science and Environmental Epidemiology)

However, an important distinction emerged between mean exposure and cumulative exposure, which takes the duration of the commute into account:

Longer commute times, regardless of route type, tend to increase cumulative exposures; this difference was especially evident for cycling. Even though cyclists’ mean particulate exposures were reduced on alternative routes, the longer duration of these routes increased cyclist’s cumulative exposures relative to driving.

In other words, simply avoiding routes with high vehicle traffic wasn’t enough to eliminate cyclists’ exposure to air pollution. Since these alternate routes took longer to bike, the increase in cumulative exposure offset some of the reduction in mean exposure. Bikers also breathe heavier and faster than other commuters, which “probably results in at least a doubling of their estimated inhaled exposure relative to driving,” according to the authors.

Even so, you shouldn’t ditch the bike. “The benefit of increased exercise is likely to outweigh the risks because of increased air pollution intake,” the authors write. But their findings do reveal an “important uncertainty” in the net health impacts of cycling versus driving—one that planners should consider at the infrastructural level.

Although Fort Collins is an exceedingly bike-friendly city, its cycling infrastructure consists mostly of on-road bike lanes—meaning cyclists are still exposed to a lot of car traffic even when they take alternative routes instead of main roads. The researchers suggest that cities could achieve larger reductions in pollution exposure by building greater separation between cyclists and drivers—for example, with off-road, multi-use bike paths. Far from negating the benefits of cycling, the Fort Collins study argues that more—and smarter—cycling infrastructure is needed.

H/t Medical Xpress

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