Dear Umbra,

My question regards my daily half-hour (each way) bicycle commute through fairly heavy city traffic. I’ve been wondering if the benefits (exercise, sunshine, free and fast transport) are outweighed by the negatives (primarily breathing in diesel and other exhaust, but I’d also throw in the risk of almost getting run over, despite the cheap thrills).

I am fortunate enough that my alternative would be to take the subway, not drive. Perhaps you could comment on the personal and environmental health effects of different types of commutes.

Washington, D.C.

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Dearest Indie,

Spoke truth to power.

Biking, biking, we love biking.

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You have two questions here. The first is whether you are hurting your health by biking in traffic. The second is a health comparison between the bike and other modes.

Clearly, biking not only maintains but improves your general physical health, in terms of muscles and heart rate and mental peace, and has little impact on the environment. It beats motorized vehicles — or, as I like to call them, Mobile Emissions Sources — of all types on both these counts.

Being near or in traffic has an impact on our health and the environment, no matter what vehicle we choose. Chemicals and particulate matter flow from car and bus and taxi engines and into the mini-weather system of the traffic zone. These nasties include carbon monoxide, the BTEX volatile organic compounds (benzene, toluene, ethylbenzene, and xylene), and nitrogen oxides. Yummy.

The nasties are densest at the middle of the traffic zone, and less intense on the edges. So, to put it simply, the position of your lungs is key. Of course, there are many variables for air-pollution scientists to play with, and each situation is different, and so on — but, basically, studies show you get the biggest hit of the nasties when you’re inside a car. Sure, a personal Mobile Emissions Source appears hermetic, but it’s an illusion: MES occupants are very close to sucking on the tailpipe of the MES just ahead of them. In a bus, riders’ lungs are a bit above these sources. And bikers and pedestrians are on the outskirts.

The little information I was able to find on subways compared them to buses. Pollutants in the subway tunnel are fairly equivalent to bus pollutants, so I will extrapolate that biking wins over all mechanized transport. And that, very briefly, is the answer to both your questions. While you may be hurting your health by biking in urban traffic, you are not hurting it as badly as you could be.

Now be careful out there!