Some Thoughts on Near Roadway Air Pollution and L.A.’s Future

From Rob McConnell's presentation: air pollution spikes at freeways
From Rob McConnell’s presentation: air pollution spikes at freeways. Pollution levels drop quickly away from freeways.

I attended a forum event yesterday, entitled “The Collision of Best Intentions: Public Health, Smart Growth, and Land Use Planning.” Speakers focused  on “NRAP” – an acronym I wasn’t familiar with. NRAP stands for Near Roadway Air Pollution. It’s the study of pollution risks near freeways and other high-volume roads.

I confess that I have been only vaguely aware of NRAP. Years ago, I had heard about studies that show health issues correlate to areas close to freeways. I vaguely recall some efforts to keep schools at a tolerable distance from freeways. I am still not all that up to speed on this issue, so apologies if I have characterized anything incorrectly in this article.

The fundamental question that this conference explored was, basically: In the light of air pollution issues, is urban densification good for overall health? There are a number of corollary issues: On congested-polluted streets, is bicycling or walking healthy? Is Transit-Oriented-Development, or, more generally, infill development bad for our health?

For me, a car-free bike activist, these questions go to my fundamental core. Of course bicycling and walking are good! For me, for my community, my planet. I think that there’s a body of research that backs me up. Cyclists live longer than non-cyclists. Health benefits of cycling outweigh risks by 20:1, according to a London study. Inactivity is dangerous, in the long run. There’s also research showing that car occupants are exposed to unhealthy air quality inside cars, so, even if bicycling exposes me to roadway air pollution, I don’t think I am at any greater exposure than other folks using the road. And cyclists and pedestrians are on the edge of that pollution cloud, not in the thick of it the way drivers are.

I suspect that a lot of people make poorly informed decisions based on perceived risk. The most common example is that of the person who drives to their destination because they afraid of flying. Flying is, statistically mile-for-mile, way safer than driving.

I haven’t seen a clear study on this, but I tend to think that a similar ill-informed trade-off takes place with driving and bicycling. Replacing a perceived-dangerous ~10mph bicycle trip with a perceived-safe 50+mph car trip may well put a well-intentioned person at greater risk. Not bicycling in a polluted city, while instead driving in a polluted city doesn’t make good sense to me. My hunch is that it’s a similarly false trade-off, like driving instead of flying.

Back to yesterday’s forum.

From Rob McConnell's presentation: Asthma is worse closer to major roads.
From Rob McConnell’s presentation: Asthma is worse closer to major roads.

USC’s Rob McConnell presented on research that found clear relationships between proximity to freeways and rates of asthma and obesity. Apparently, historically, there was a general understanding that regional air pollution made asthma worse, but didn’t cause it. The current understanding is that roadway pollution causes asthma. Watch a similar talk by Rob McConnell here. McConnell also reviewed research linking NRAP with increased obesity.

These very real heath risks led researchers to investigate solutions. UCI’s Doug Houston spoke about a review of various structural tinkering to mitigate roadway pollution. Researchers have looked to soundwalls, sealed windows, taller building, vegetation, indoor air filtration, and more. Though those measures help, none of them quite solves the problem.

When there’s no airtight mitigation, health leaders turn to the solution that I mentioned above: keep people away from freeways. Don’t locate homes, schools, parks, work-sites, etc. within a 400 meter (~1200 foot) buffer of freeways.

I tend to think that this buffer approach results in a vicious cycle. Creating freeway buffers will spread things out even more, making for longer trips which are more difficult to walk and bike. Driving more for more trips increases traffic congestion. Congestion leads to road widening. Widening (and increased traffic volumes) means moving that initial buffer outward, compounding the problem.

As I was listening to all this, I felt like there was too much emphasis on dealing with our car-centric system as a given. Car-choked freeways are just part of the way god made our cities. We, health professionals, are just doing our best to adjust to the system we find ourselves stuck in. The discussion was all about how to keep people out of the way of pollution, but not to look at reducing or eliminating that pollution at its source. It’s as if health professionals looking at the tobacco problem just assumed that smoking happens everywhere, and then spent a lot of effort studying gas-masks for non-smokers. Taking on tobacco is a great public health success – because health professionals were able to ban tobacco from many places, and to stigmatize tobacco based on its threat to health.

(I also think that an overly narrow focus on near-roadway-air-pollution makes us miss other huge health risks associated with cars. Every year, driving kills 30,000+ people in the U.S., 1.5 million worldwide. There are greenhouse gases, water pollution, noise pollution, obesity, and plenty more issues.)

I was glad to hear Occidental College’s Mark Vallianatos, commenting from the floor microphone, suggest an important alternative. Instead of moving people away from roads, let’s change our roads to be safe for people. If we have schools, playgrounds, housing, etc. adjacent to a road, then, for the sake of health, let’s design and regulate that road to limit vehicle emissions to safe levels. Let’s traffic-calm and road diet our arterials, downgrade our freeways, hopefully get rid of, at least, some of them.

Reducing car capacity isn’t politically easy. It may not work everywhere right now, but, going back to what the forum was addressing, I think it’s important for our core urban neighborhoods. It’s important for the places where we’re trying to make smart growth and TOD work. If health professionals are questioning the health effectiveness of smart growth, of walking, and of bicycling, then we need to also question the unhealthy car-centric systems that surround and endanger these solutions.

  • Jake Wegmann

    Well said. This is an important debate that has just barely started to move out into the open. Michael Woo, certainly a heavy-hitter, at a TOD conference at Berkeley a couple of years ago characterized the health impacts of living right next to a freeway as the issue that planners are scared to talk about. Your way of writing about it is a useful and thoughtful way to start.

  • traal

    Given that wider freeways create more air pollution than narrower freeways, the 400-meter buffer should be proportional to the width of the freeway.

    The buffer should also be wider for heavily congested freeways.

    The way to keep the buffer at its minimum into perpetuity is either to restrict density and property rights, or to use traffic demand management (good old-fashioned supply & demand) to permanently prevent freeways from ever getting congested.

  • Juan Matute

    Doug Houston is great on this subject. The most severe knowledge gap is in understanding production and effect of ultrafine particles (aka PM1.0), which aren’t meaningfully regulated.

  • Andrea Hricko

    From Andrea Hricko, USC. So glad to have Streetsblog as part of the discussion and to have you present a poster at the USC-NIEHS community forum. We were aiming at developing a dialogue, and your post has helped that. I believe the general sense from yesterday is that TOD is terrific for improving public health (fewer cars, more walking and biking) — but that there are challenges when planners/developers put dense housing near transit stops (great) and then have the other side of the TOD housing complex be feet from a busy freeway (not so great). Thus the “collision of best intentions.” Thanks for engaging, Joe.

  • DMalcolmCarson

    I’m not sure that it negates the case for reducing the impact of freeways on communities if a decision is made not to put any more people in harm’s way. What this reinforces to me is the need to get out of the rail-centric TOD paradigm and look at developing TOD in already built up neighborhoods that have frequent bus service and/or rail stations away from freeways. In LA’s case, that still leaves plenty of territory.

  • Joe Linton

    Yes – it seems like not putting new schools/parks/etc near freeways adds more burden to communities already harmed by freeways.

  • True Freedom

    A few comments:
    a) don’t forget that even if we reduce personal transit via the auto, we still have to move goods into our dense neighborhoods. These goods are typically delivered via diesel trucks, which are far worse in damaging local air quality than the modern personal auto.. this needs to be addressed
    b) the problem is not just freeways, but all of our roadways. My workplace is in a dense section of Pasadena. I cycle there, walk to lunch, and occasionally walk/ bike for light errands. With the dense environments, we have many more cars.. moving slowly, stuck at lights, waiting for peds, stopping/ going. This is nice in one way, because we slow autos down. It is bad in another, because stop/go traffic is most inefficient.. which increases emissions, which happen to be only feet from our pedestrians and cyclists.

  • LAifer

    This study is only looking at the air pollution part of the equation of health. When you talk about sprawling out communities alongside freeways to give a buffer, you’re now also pretty much forcing all those alongside the freeways to drive or take long bike rides or walks (in that dirty air), which doesn’t help matters either. You’re either making matters worse by forcing them to breathe more air to walk or bike longer distances, or making matters worse by forcing them to drive when perhaps denser development would allow them the option to bike/ride shorter distances.

    I’m grateful that we have a clearer understanding of the direct impact of these vehicular rivers on our health and well-being, but I think Joe’s critique of the policy solutions contemplated by the study’s authors is spot on, in that they assume drivers will always be there driving. Yes, there’s need for shipping/trucking, but that’s true the whole world over, and you don’t see the volume of traffic in other developed parts of the world that you see here. It’s possible – we just need to think more globally about policy rather than just trying to fix one problem at a time with ideas like spreading out development within a band alongside sides of freeways.

  • DMalcolmCarson

    Again, I wouldn’t say that. Of course it depends on how you define the geographic “community” but if we’re talking really about +-500 feet from a freeway, the vast majority of all of LA’s communities still fall outside of that, and for those who are within that, having a park to go to outside of that is still a benefit, as long as it’s not too far.

  • Kevin Love

    Far more lethal and deadly cancer-causing pollution is caused by car drivers on local streets. I don’t live on a freeway. I do live on a local street. Every day I can see car drivers launching their lethal cancer-causing poison attacks upon myself, my wife and my children.

    In my opinion, one of the best jobs of analyzing the health impacts of these lethal cancer poison attacks has been done by the City of Toronto by their Public Health Department led by the City’s Medical Officer of Health, Dr. David McKeown. The results are, quite frankly, profoundly disturbing. Equally disturbing is the lack of a similar report for New York. See:

    An excerpt from the Report:

    “The current study determined that traffic gives rise to about 440 premature
    deaths and 1,700 hospitalizations per year in Toronto. While the majority of
    hospitalizations involve the elderly, traffic-related pollution also has
    significant adverse effects on children.

    Children experience more than 1,200 acute bronchitis episodes per year as a result of air pollution from traffic. Children are also likely to experience the majority of asthma symptom days (about 68,000), given that asthma prevalence and asthma hospitalization rates are about twice as high in children as adults….

    …mortality-related costs associated with traffic pollution in Toronto are about $2.2 billion.”

  • Alex Brideau III

    True. While not directly discussed, all roadways add to air pollution, not just freeways. While efforts should continue in getting people out of cars, those cars, trucks, and buses that remain need to transitioned to lower- and zero-emission vehicles on an expedited basis.

  • Alex Brideau III

    I’ve heard of a good number of carless streets out there. Has anyone heard of streets that only allow zero-emission vehicles? Might be an innovative, if controversial, initiative in certain neighborhoods.

  • Alex Brideau III

    The reference to the NSC’s “Odds of Dying from…” numbers ( was interesting. I see references to death by motor vehicles, air/space transport, and even motorcycling, pedalcycling, and walking. But I can’t see any stats on deaths by rail accidents. Are the odds of dying in a rail accident so remote they are off the charts?

  • True Freedom

    this is one of the main reasons that I live in a very low density neighborhood … lot’s are a minimum of a half acre and increase to several acres. Our yard and local park have very few autos within a half mile radius, which is the best I can do for my three young children.

    I ride my bike into the denser parts of town for work and shopping.

  • Joe Linton

    Basically yes – I need to pull out the book “Car Free Cities” – but rail passenger deaths in the 20th century I think were less than 100,000 – don’t quote me on that – lemme check. Here’s a link to federal data – most years it’s in the single digits: – compare to 30,000+ annually

  • True Freedom

    I havent’ seen stats for 500ft, but have seen the stat that 50% of Angelenos (10M people) live within a mile of a freeway.

    Unofficially, I’d say that everyone lives within 500ft of a road, tho

  • DMalcolmCarson

    Well 500 feet is less than a tenth of a mile, so that would be less than 5% of Angelenos living within 500 feet of a freeway. It’s probably a higher percentage of low-income people though.

  • Kevin Love

    Yes, there are places with streets that only allow zero-emission vehicles. Provided that the vehicle is a bicycle. Here is a look at North America’s largest urban car-free zone. See:

  • Kevin Love

    Fortunately, we already have those vehicles and their infrastructure. They are called “railways.”

    Railways would be carrying a lot more freight if truck drivers had to pay the maintenance costs their trucks impose on the roads. Those costs are picked up by the hard-working taxpayer. But rail maintenance costs are (mostly) not.

    That’s an unfair socialist subsidy. Time for trucking companies to stop being corporate welfare bums. As a fiscal conservative, I believe that these freeloaders should start paying their way.

  • Alex Brideau III

    Cool! Any streets you’re aware of that allow only zero-emission motor vehicles?

  • Kevin Love


  • SZwartz

    That is the reason that there is a worldwide consensus that wherever possible Bike lanes should not be on major boulevards. The health risks to the individual bikers is too high. Bike Lanes need to be located away from the major boulevards.

  • SZwartz

    And thereby undo a considerable amount of the protection you had by living in a less dense area unless your bike route avoids major boulevards.


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