Lesley McClurg traveling to KQED on her bike. (LindseyHoshaw/KQED)

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The traffic in the Bay Area regularly ranks among the nation’s worst — and sitting in traffic isn’t just irritating; there’s some downright unhealthy stuff in that air you’re breathing.

Breathing in air pollution can irritate the lungs and aggravate both asthma and cardiovascular disease. However, a recent study from the California Air Resources Board shows that how you get to work makes a big difference.

Commuters participating in the study wore backpacks crammed with instruments to measure soot from diesel engines and other pollution while they biked, drove, bused or rode the train to work in Sacramento.

I decided to try it on my own daily commute from Oakland to San Francisco, using the same gear borrowed from the Air Resources Board. Over the course of a few days I measured the pollution while I biked, then rode BART, and finally drove to my office. Even though my little experiment was clearly not scientifically significant, the results generally matched what the researchers found in Sacramento.

Lesley McClurg preparing air pollution measuring devices before her morning commute.

BART was the clear winner for  me. Light rail also exposed Sacramento commuters to the least polluted air. Driving came in second for me, and biking exposed me to the most smog. The researchers found pollution levels to be pretty similar for cars, buses and bicycle trips.

I didn’t take a diesel-powered train, but the Air Board noted that older Amtrak trains on the Capitol Corridor exposed participants to the worst air. However, Amtrak is updating its locomotive fleet with newer models, so future trips should be a lot cleaner.  Incidentally, high-speed Rail, when in service, will be even cleaner.

Fortunately, none of the pollution levels I recorded during my commute — biking or driving — were dangerous. Study participants in Sacramento were also well within safe exposures.

A street-by-street look at pollutants in San Francisco and Oakland. Aclima and Google plan to soon offer an interactive map where you can click on a particular street for more detailed information. To learn more.

Below is a list of ways to protect yourself from nasty air while taking various forms of transportation.

1) Travel by Light Rail

My trip on BART from Oakland to San Francisco offered the best air. In general, the Air Board found electrically powered light rail to be the cleanest mode of transportation. That’s likely because the trains themselves do not release any exhaust. However, the researchers cautioned the results may be different if the route is near a freeway.

2) Set the AC to Recirculate

My car trip was the second best. The Air Board said turning the air-conditioning on and setting it to recirculate (versus pulling in air from outside) can reduce pollution levels by up to 75 percent. In other words, roll up your windows and prevent as much air as possible from entering when driving through congestion.

3) Cycle On Bike Paths

As an avid cyclist, I was disappointed to learn that I was exposed to the dirtiest air while on two wheels. I’m going to try to find a less congested route because the Air Board says you can greatly reduce air pollution simply by cycling a block off a busy road or on bike paths away from heavy traffic.

4) Avoid Exhaust

Researchers found that commuters taking diesel trains were exposed to the worst air over other modes of transportation. It’s best to avoid older diesel-powered trains that push rail cars, which were worse than engines that pulled cars. If you must take an older train, try to get a seat in a cabin away from the locomotive engine.

5) Check the Air Forecast

Air quality can change day-by-day and block-by-block. It’s a good idea to check the current pollution levels before deciding what mode of transportation to take. You can check your neighborhood at airnow.gov, or sparetheair.org. This is especially important when there is a wildfire burning in the region or a temperature inversion layer puts a lid on the area, preventing pollutants from escaping.

6) Carpool

Sharing a vehicle not only shortens the trip because you can zip along in the carpool lane, it also means you’re on the road for less time breathing bad air. Plus carpooling is a win for everyone because it means fewer cars are on the road spewing emissions and adding to congestion.

Bike, Car or Train: Which Commute Has the Worst Air Pollution? 21 November,2017Lesley McClurg

  • Louisla4

    Always thought it was counterproductive seeing people jogging along major roadways. People are social animals and like to be seen. I live along Sir Francis Drake Blvd. in Marin. After opening our front (road-facing) screened windows on the first hot day in residence here, the apartment was filled with a fine dust from….pollution and the motion on the roadway?…all the cobwebs became visible. Never open the front windows anymore.

  • Dave Vernon

    When taking Caltrain, which utilizes a combination of old and newer diesel engines, it depends on the direction you are traveling that determines whether it is a push or pull configuration. Northbound trains always push, and Southbound train pull. I cannot comment on any difference between fuel usage between the two, but seems to me that being on a push train would be best, as the train cars are generally moving away from the exhaust path. I concur that being furthest away from the engine in either circumstance would be preferable.

    • jaworskir

      Dave, thanks for bringing this up. I, too, commute on Caltrain, and on my afternoon southbound journey, if I get a seat in a car right behind the engine, I definitely can smell diesel exhaust in the cabin. Staying far to the rear on southbound runs would be better. I also agree that northbound is better since the exhaust trail is behind us.

  • JonDubno

    BART is “light rail”?

  • bc

    Did she drive w/ recirculate AC on? That’s the way I almost always drive even tho. it’s very expensive in gasoline and electricity. (Prius and now P. Prime). And no mention of soil dust. Here in Salinas the ag. industry is extremely polluting, except in wet weather. I can smell the dust when windy, and a clean in appearance ‘bile requires wash at least twice a week! In the Summer I run window fans overnight to cool for the next day. The filters are soon caked w/ soil. Finally, when will the EPA require exhaust converters (Diesel) that oxidize, so no carbon particles? (No political comment follows.)

  • solodoctor

    The tip about setting the AC to recirculation is a good one. Thanks!

    BART is good but limited because it only provides access to the Market St corridor in SF. Then one has to take MUNI to get to other parts of the city. That can take a lot more time than driving.

  • IdleFree

    It’s important to note that the A/C does not have to be on (such as in cooler weather) to use recirculation. Be ready to hit recirculation in the unlikely even of being coal-rolled (diesel pickup truck purposely emitting great amounts of black soot). In newer vehicles, recirculation prevents about 80% of tailpipe emissions from entering the cabin.

  • Sutekh

    Is there actually a state where bicyclists on the road actually obey traffic laws?

  • saimin

    Which commute causes the most pollution?


Lesley McClurg

Lesley McClurg reports for KQED Science primarily on medical and mental health with a sprinkling of stories about space, environmental toxins and food.

If there’s a natural disaster brewing Lesley can usually be found right in the midst of a catastrophe. She’s reported on disastrous floods, fires, droughts and earthquakes.

Her work is regularly rebroadcast on NPR and PBS. She is an Edward R. Murrow and Emmy award winning journalist. The Society of Environmental Journalists recognized her beat coverage of California’s historic drought.

Before joining KQED in 2016, she reported for Capital Public Radio, Colorado Public Radio, KUOW and KCTS in Seattle.

You can find her on Twitter at @lesleywmcclurg.

You can find her KQED medical science stories, her environment stories, and general news stories.