People who move to the suburbs may think they’re fleeing the polluted air of the city.  Of course, there’s a tradeoff: by living in low-density suburbs, they spend more time in their cars. And as it turns out, the air inside your car may be just about the dirtiest you’ll breathe all day.

Last year, researchers in Sydney, Australia released a study (pdf) that measured the levels of benzene (a carcinogen) and other volatile organic compounds (VOCs), as well as asthma-inducing nitrogen oxides, among people who commute by car, bus, train, bike and foot.

The verdict? Car commuters breathed the worst air, getting the highest doses of benzene and other VOCs. Even bus commuters were exposed to lower levels of VOCs than car commuters (though bus riders breathed higher levels of nitrogen dioxide). Train commuters had the least exposure overall, with cyclists and walkers coming in second-best.

  • One reason for the difference is that motorists are breathing exhaust, both from their own vehicles and from nearby traffic. As the authors of the Sydney study note, driving on congested freeways puts motorists in a "tunnel of pollutants." By contrast, other travel modes reduce ambient exposures: trains tend to run on isolated tracks, buses often take express lanes, walkers and bikers may travel on quieter streets.

    The US census says that 87.9% of Americans commute by car, truck, or van, and the National Household Transportation Survey shows that people who live in sprawling suburbs spend about 68 minutes per day in their cars—about 50 percent more than people who live in more compact urban neighborhoods.

    So, to some extent, if you want more fresh air it may be smarter to move closer to downtown, rather than farther away.