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June 30, 2005

Waiting to Inhale

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.

Posted by Jessica Branom-Zwick | Permalink


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Good post-- reason # 25395 to bike or walk. Yet I wonder how particulate matter stacks up by mode. The Copenhagen Post published an interesting, albeit brief, article today on white blood cell damage in cyclists (3x greater on streets than indoors). The smoking gun? (You'd never guess). "Cars are to blame."

What's more disconcerting is that the mode split in Copenhagen is substantially more bike/ped heavy than in places like Seattle (for now)-- and thus, my blood's *really* boiling.


Posted by: John M. | Jul 1, 2005 10:38:48 AM

I think an interesting line of study would be to follow up on this: "Walking and cycling are likely to be most beneficial when routes are away from busy car routes, although even on the same roadway and taking into account increased respiration due to activity, cyclists in Amsterdam still had 2-3 times lower exposure to pollutants than car drivers."

I would have assumed that the car would shield the driver and passengers from a lot of the pollution, and that a biker would have to suck it up directly. It seems weird to me that this isn't the case, particularly for bikers riding directly in the lane. This is maybe explained by the pollutants being trapped inside the car with its occupants.

Posted by: Uncle Vinny | Jul 8, 2005 6:21:09 PM