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Take the Easy Way

2010 December 15

My commute to work follows one of the finest urban bike paths in the country on the Capital Crescent Trail , a converted rail line running from the Maryland suburbs to the edge of downtown Washington, DC.  I am asked on occasion if I worry about breathing exhaust while on my bike.  With plenty of time in the saddle to think it over I started wondering: how is the air today?  That’s a question anyone can easily answer thanks to the Clean Air Act amendments of 1990.  One of the benefits of the landmark legislation was the expansion of air quality monitoring and the publishing of such information widely.  Today, I subscribe to EnviroFlash email alerts and get a daily forecast of air quality for the next three days.  I like to get their “Air Quality Notifications” in my inbox before I go out for a ride.

Metro Washington, DC did not see a single ‘code red’ (very unhealthy) alert in 2005 for the first time since the color system was inaugurated.  This doesn’t mean the problem is solved, however.  Over the summer of 2010 there were several ‘code orange‘ (unhealthy to sensitive groups) and ‘red’ events.  The negative effects of poor air quality on human health, over the long term, are indisputable but these alerts are based on ambient air quality.  Your personal exposure depends on a variety of factors and one of these is how you get to work.

When the morning weather report indicates the air quality forecast is not coming up ‘green’ you might think that driving your car is your best alternative.  After all, if it’s summer in DC you’ve got the windows rolled up and the air conditioner blasting.  But studies comparing different modes of transportation have found that driving a car does not mean you’re breathing fresh air.  A 2000 report by the International Center for Technology Assessment found that ‘in car’ air quality by a number of measures is worse than the ambient levels outside.  And the pollutants of concern, such as fine particulates and carbon monoxide, are not something your car’s air conditioner will filter out.

A 2004 study in Sydney found automobile drivers’ exposure, measured by personal monitors, higher than cyclists and walkers in all five pollutants.  The researchers noted that one explanation may be the “tunnel of pollutants” effect on a busy road where your vehicle’s air intake is taking in the exhaust of the cars in front of you.  The test subjects in Sydney followed their usual commuting pattern.  Cyclists, by favoring streets with less traffic, lowered their exposure compared to drivers.

A more recent 2007-2008 study undertaken in the Netherlands compared car, bike, walking, bus and train transportation modes along the same routes.  For contrast, they also included a low-traffic bike route.  The results emphasize two points of importance to urban cyclists.  Using heart rate monitors the researchers found that bike commuters respirated at about twice the rate of car and bus passengers.  This is normally a good thing and one of the health benefits of biking.  But on the high-traffic route this also meant the cyclists had the highest inhaled doses of some pollutants.  The lesson for cyclists from the Netherlands study is to take the easy way.  Pick your route carefully and avoid busy streets whenever possible.  Cyclists on the high-traffic route had an exposure level 40% higher than the low-traffic alternative.  In other words, cyclists can significantly reduce their dosage by riding off road or on the least busy streets possible.

Back home, two decades after the Clean Air Act amendments of 1990, the air quality in metro Washington, DC continues to improve but we still are not meeting the federal standards.  This past summer there were several times I did not to ride due to ‘code red’ forecasts.  When you ride, keep your head up and look for ‘greener’ days ahead.

For further reading:

Comparison of air pollution exposure for five commuting modes in Sydney – car, train, bus, bicycle and walking (PDF)

Commuters’ exposure to particulate matter air pollution is affected by mode of transport, fuel type, and route.

All-cause mortality associated with physical activity during leisure time, work, sports, and cycling to work.

In-Car Air Pollution The Hidden Threat to Automobile Drivers

Peter Kokopeli is a senior environmental protection specialist with the EPA’s Clean Air Markets Division in Washington, DC.

Editor's Note: The opinions expressed here are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.

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