How Close is Too Close to Live by the Highway?

More and more people are living, working, and going to school close to the freeway. But how close is too close?

Sabrina Stierwalt, PhD
4-minute read
Episode #275

In Southern California, an estimated 1.2 million people live within 500 feet of the freeway even though the California Environmental Protection Agency and the California Air Resources Board recommend against it. As urban populations rise around the globe, more and more people are living in zones with high levels of air pollution close to major roadways. Many of those people have fewer economic options making freeway pollution a matter of environmental justice.

The health risks of living, working, or otherwise spending large fractions of time near freeways, are a topic of current scientific study but are already known to be numerous. For example, children living close to freeways have higher rates of uncontrolled asthma and other respiratory problems. A decade-long study of adults living in Ontario, Canada, revealed an increased risk of dementia for residents closest to the freeway. The same study found no link to higher rates for the less common Parkinson’s or multiple sclerosis, although experts note this could be due to the lower numbers overall for these conditions and that further study is needed.

Residential proximity to the freeway has also been linked to cardiac issues. The build up of carcinogens in the bloodstream can elevate cholesterol levels in the short term and possibly lead to heart attack or stroke in the long term. Lower bone density in adults and lower birth weights may also be linked to freeway proximity.

How Can You Protect Yourself from Highway Pollutants?

If logistically and financially possible, live, work, and go to school outside of the 1000-foot zone within the freeway where traffic pollution is typically highest. However, not all freeways are equal offenders. Areas near freeways frequented by diesel trucks are exposed to the worst kinds of carcinogens that are linked to the bulk of associated cancer risks. Warehouse distribution centers and ports should also be avoided for similar reasons.

Interchanges and areas where braking is more frequent are also worse than average because they combine pollutants derived from exhaust with other pollution sources like the toxic metals found in the dust from brake pads and tires. These so-called non-exhaust pollutants are the main reason a shift toward electric cars will still not entirely solve our air quality problems.

When calculating distance from a freeway, elevation may also matter. Although common sense may suggest that a freeway that is far below or above where people spend most of their time may help to improve air quality, there is so far little evidence that such a height difference helps. In particular, corridors of tall buildings can be very effective at trapping polluting particles near people’s lungs. For this reason, the San Francisco Health Code still requires ventilation for all units in a multi-story building and not just those at street level. For regions closest to freeways, pollution may be lower when the landscape includes buildings of different heights as well as parks and other open spaces where pollutants have escape routes.  

If you live in southern California, you can find out how far your home, school, or office is from the freeway using a mapping tool provided by the LA Times. And take a look at their pollution map.


About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.

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