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In a Jockology column last summer, I described a few studies about how switching from car to bike for a commute affects your exposure to pollution:
Whether you’re better off inside or outside a vehicle seems to depend on the vehicle and location. A Danish study in 2001 measured pollution exposure while driving or biking along identical routes in Copenhagen. The air inside the cars was bad enough that, even taking into account that cyclists were taking longer and breathing more deeply, the drivers were worse off. On the other hand, an Irish study in 2007 found that the air on buses was worse than the air breathed by cyclists, but that the higher breathing rates led to greater total exposure for cyclists.
It’s one of those issues that might make you think twice about cycling through a busy downtown core to get to work — that, and the risk that you’ll be flattened by an impatient driver. There’s an interesting study that just appeared online in the journal Environmental Health Perspectives weighing the balance between cycling and driving in cities (the full text is freely available here). They make an interesting distinction between what’s good for society and what’s good for you:
Though society may benefit from a shift from private car use to bicycle use (e.g. because of reduced air pollution emission), for the shifting individual disadvantages may occur. While the individual may benefit from increased physical activity, at the same time he/she inhales more pollutants due to an increased breathing rate. The risks of getting involved in traffic accidents may increase as well as the severity of an accident.
To tackle this question, the researchers (from the University of Utrecht) crunch an enormous data set to determine what would happen if 500,000 people switch from car to bike for short trips in the Netherlands (though they argue that the conclusions are widely applicable in other countries). They use demographic information along with studies on air pollution, traffic safety and physical fitness to reach the following encouraging conclusions:
For the individuals who shift from car to bicycle, we estimated that beneficial effects of increased physical activity are substantially larger (3 – 14 months gained) than the potential mortality effect of increased inhaled air pollution doses (0.8 – 40 days lost) and the increase in traffic accidents (5 – 9 days lost). Societal benefits are even larger due to a modest reduction in air pollution and greenhouse gas emissions and traffic accidents.
One of the interesting points that emerges in their discussion of the pollution studies is how big a difference your route choice can make (which I also discussed in the Jockology article linked above). In fact, they cite one study that found “walking close to the kerb in London greatly increased personal exposure”!