Traffic: On the Road, and in the Lungs

I’d ban all automobiles from the central part of the city. You see, the automobile was just a passing fad. It’s got to go. It’s got to go a long way from here.
~Lawrence Ferlinghetti

Both at work and on teh interwebz, people are full of tales and advice about how to be green and reduce one’s carbon footprint. Although I cannot recall asking for advice on becoming less of an environmental insult, I receive it fairly frequently, usually in the form of “you oughtta.” “You oughtta become a vegan”, or “You oughtta stop using air conditioning, even when it’s eleventy hundred degrees in the shade”, or “You oughtta hand-wash and air-dry your gross anatomy scrubs”, or “You oughtta grow everything you eat.” The only suggestion that does not make me roll my eyes and think get realz, is “You oughtta ride your bike to work.” This last dictate is within the realm of possibility, at least when there’s not major construction along the shortest route to work, and in fact the construction, when completed, might make cycling along the route safer. At the moment, there are 8-inch dropoffs into trenches filled with rebar, metal mesh, and broken concrete.

I live just over six miles from the medical center where I work, and typically leave home early enough that I don’t have to spend much time stuck in traffic. With the current construction, though, I often have to take a slightly longer (eight miles) route to and/or from work, and as most of it is along a very busy state highway, it’s not suitable for cycling. But I do feel vaguely guilty about my commute, even though I drive a fuel-efficient Honda, and try to complete shopping errands on the route home. The internal combustion engine is undeniably bad for air quality, something I know anecdotally from dissecting the lungs of former urban dwellers, in gross anatomy lab. Many of the students, expecting perfect pink lungs in the thorax of a non-smoker, are surprised by the dark inclusions scattered across most cadaveric lungs. “I think this person was a smoker!” … no, smokers’ lungs look like something you’d empty out of the charcoal pan of your backyard grill (unless you’re a raw foods vegan and never grill anything, of course).


Air pollution, Victoria Harbor, Hong Kong
Photo by Yym1997, under GNU Free Documentation License

The US Environmental Protection Agency regulates particulate matter (PM) defined as “inhalable”, i.e. coarse particles between 2.5 and 10 micrometers in diameter, and fine PM, less than 2.5 micrometers in diameter, both of which can penetrate into the lungs. Most fine particle pollution in the US consists of secondary particles, which form through atmospheric reactions of sulfur dioxides, nitrogen oxides, and other compounds emitted by industries, power plants, and motor vehicles. Particulate matter is one of six pollutants for which there are National Ambient Air Quality Standards, under the Clean Air Act in the US. The EPA lists a number of health effects from exposure to inhalable particle pollution, including airway irritation, decreased lung function, aggravated asthma, and nonfatal heart attacks. Chronic exposure to particulate matter can be assessed by measuring the carbon load of airway macrophages, collected in sputum samples; this carbon load is correlated with the proximity of a person’s residence to busy, major roads. Using this approach, Jacobs and colleagues (2011) showed that in nonsmokers with diabetes, higher levels of oxidized low-density lipoprotein (LDL), a biomarker for atherosclerosis and arterial plaque formation, were associated with increased carbon load in airway macrophages. Particulate matter from traffic affects the health not only of the lungs, but the of cardiovascular system as well.


Air pollution, Eiffel Tower, Paris, France
Photo by ILJR, under GNU Free Documentation License

If one is concerned about exposure to inhalable particle pollution, what is the best way to commute to work (given that telecommuting, e.g in a wearable office such as cromercrox’s, is ideal, but not possible for everyone)? Two recent studies in the Netherlands address this modern eco-quandary. In Arnhem, a medium sized Dutch city, Zuurbier and colleagues (2010) measured exposures to inhalable coarse and fine particles and to soot in diesel- and gasoline-fueled cars, in diesel and electric trolley buses, and along two bicycle routes with low and high traffic intensities. Inhaled doses of air pollutants were estimated, based on the heart rates and ventilations per minute of healthy volunteers in each of the transport modes. Not surprisingly, inhaled pollution doses were highest for cyclists along high-intensity traffic routes, but these researchers argue that the positive health effects of cycling outweigh the negative effects of inhaled pollution.

A different approach, using life table calculations to determine mortality impacts in life-years gained or lost, when transitioning from car to bicycle for daily trips, yielded the same basic conclusion. In a 2010 paper, de Hartog and colleagues focused their quantitative comparisons of driving vs. cycling on air pollution exposures, road traffic injuries, and physical activity. Of course, estimated inhaled air pollution doses and risks of a fatal traffic accident are higher for cyclists than for drivers. On the other hand, the health benefits of physical activity, including decreased cardiovascular disease and mortality, are substantial for cyclists. The researchers calculated a gain of 3 to 14 months from the increased physical activity, which outweighs the potential mortality effects from inhaled pollution (0.8 to 40 days) and increased traffic accidents (5-9 days). Switching from driving to cycling has societal benefits too, with decreased air pollution in urban areas, and might lead to changes in urban planning, such as inclusion of more bicycle routes and lanes. Athene recently described her ability to commute by bicycle in Cambridge; with developments of greenway trails and bicycle lanes in my own city, I hope to be able to commute to work safely by bicycle in the near future.


de Hartog JJ, Boogaard H, Nijland H, Hoek G (2010) Do the health benefits of cycling outweigh the risks? Environ Health Perspect 118, 1109-1116. doi:10.1289/ehp.0901747

Jacobs L, Emmerechts J, Hoylaerts MF, Mathieu C, Hoet PH, Nemery B, Nawrot TS (2011) Traffic air pollution and oxidized LDL. PLoS One 6(1):e16200. doi:10.1371/journal.pone.011.6200

Zuurbier M, Hoek G, Oldenwening M, Lenters V, Meliefste K, van den Hazel P, Brunekreef B (2010) Commuters’ exposure to particulate matter air pollution is affected by mode of transport, fuel type, and route. Environ Health Perspect 118, 783-789. doi:10.1289/ehp.0901622

This entry was posted in urban public health and tagged , , , . Bookmark the permalink.

8 Responses to Traffic: On the Road, and in the Lungs

  1. cromercrox says:

    My Wearable Office(TM) will soon revert to its original function of Cupboard Under The Stairs. A Slightly Larger Office is being Thought Of. Just so you know.

    • KristiV says:

      That’s good news! Though I liked the concept and whimsy factor for the Wearable Office (TM), to be honest.

  2. ricardipus says:

    For those of us a bit too far from work to cycle, or who don’t really have the option to shower and change once arriving, I guess public transport would be the “best” option (short of telecommuting I suppose).

    Problems with this solution arise in this neck of the woods, however, mainly due to infrastructure not quite keeping pace with suburban development, and the resulting economic knock-ons:

    – not enough parking near the train stations
    – poor public transit (bus) integration with other public transit (trains)
    – fares that approximate per-day parking tariffs downtown
    – trains during rush hour, but not extending *quite* far enough into the morning to allow, say, the dropoff of Junior Ricardipi at school before catching them

    I drive every day, and I dare say that many of those days I could make the effort to take the train (when not needing to drop the JR’s off at school as noted above). But if municipalities put barriers up, even little ones (fares a bit too high, somewhat annoying parking, schedules that don’t quite work), even mostly-unselfish people like me may very well choose to drive.

    And don’t talk to me about carpooling, because in the real world, it doesn’t work. None of my neighbours (a) work near me, (b) leave the house when I do, or (c) have predictable enough schedules (I’ll include myself here) to allow for it.

    Sorry, Mr. Negativity here will go and do something shiny and happy now.

    • KristiV says:

      I hear ya, ricardipus. The most direct bus routes for me were eliminated several years ago, and my only option for public transport would be to spend a minimum of three hours per day commuting on the remaining routes. That’s a deal-breaker. I carpool very occasionally, but usually my early meetings and lectures (6:30 and 7:00 AM) make me an undesirable carpool partner. I don’t have to worry about transporting any juniors or juniorettes, but that’s certainly an issue for several of my friends at work.

      My father carpooled for many years, when we lived in an inner suburb of Houston, and he and a near neighbor worked near the medical center. Although both my parents worked in or near the medical center, their differing schedules didn’t allow them to carpool, however.

  3. Interesting analysis. I’ve never really thought about all the gunk I inhale while cycling; except for a few weeks most summers, the air never looks polluted here – not the same way it does in LA, for example* – but that’s not to say that I’m not damaging my lungs by inhaling invisible particulates. I stay off the main roads, but they’re only a couple of blocks away from my route, and there are still cars on the roads I take. I do occasionally see people wearing smog masks to cycle, but I think I heard they’re not actually all that effective, and they reduce your air flow.

    A few years ago there was a bog fire just outside of the city, and the air pollution was so bad for that week that I couldn’t cycle. I got to work OK one day, but coming back up the hill, taking in massive lungfuls of air, I started coughing so badly I had to get off and push. I stuck to the bus until the rain brought the crud out of the air! I couldn’t imagine cycling in conditions even half that bad on any kind of long-term basis.

    *I remember taking off from LAX once over the ocean; when the plane turned back around to head to London, the dome of yellow-brown smog over the city was absolutely disgusting. I’ve never seen anything that bad when flying in or out of Vancouver.

    • cromercrox says:

      I’ve seen LA just like that, from the air. But that’s nothing compared with Mexico City. Many years ago when the world was young (OK, it was 1994) I spent two fabulous weeks in Mexico on assignment for Your Favourite Weekly Professional Science Magazine Beginning With N. Everything, but everything in Mexico City is brown, and they say (or did back then) that just walking around breathing in M. C. is like smoking two packs a day. You’d never know, from the smog, that looming over Mexico City are two of the biggest volcanoes in the world. One is called Popocatapetl, and the other isn’t. Notwithstanding inasmuch as which, you just can’t see them through the haze.

  4. KerstinH says:

    When I read stories like this, I realize how lucky I am.

    I have never owned a car. Not out of environmental concern. I do have a license and I do quite a bit of driving for my job. But to own a car, for me, is just not practical. I have a bike. I use public transport. I live in the city and close to work.

    The city is Berlin and it seems to me that this place is actively, though by no means intentionally, discouraging car ownership. Driving is a pain. Parking is not only scarce, but with the many construction sites migrating through this city according to some secret masterplan, you inevitably one morning will find your car towed and dumped at an obscure community center at the other side of town. Forced to regularly park in dimly lit side streets near the train tracks, your chances of smashed windshields and looted glove boxes are greatly increasing. And in winter, no matter how little it snows, road traffic will collaps anyway.
    All this, I can do without.
    But apparently I am a bit of a wimp. Because millions of fellow-citizens don’t seem to mind…

  5. Pingback: Bragging Rights Central: new archive post | VWXYNot?

Comments are closed.