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.

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Keep in mind, however, that wind patterns, temperature fluctuations, and traffic patterns all influence how far pollution can reach even beyond the highest pollution zones. You may think that pollution risks are lessened at night when there are fewer cars on the road, but in fact the opposite is true. The cooler night air is also typically more stagnant which ends up trapping pollution near the ground. One study, co-led by Suzanne Paulson, UCLA professor and Director of the Center for Clean Air, found freeway pollutants traveling as far as 4,920 feet downwind in a southern direction at night but only 650 feet in the daytime downwind (at that time northward) of CA State Route 91.

Pollutants tend to thus extend their reach the furthest during early morning hours reaching distances of sometimes more than a mile from the freeway. Thus, higher levels of air pollution are observed in the winter when later sun rises mean the early morning hours overlap more with rush hour traffic. To protect yourself, avoid going for long runs or doing other outdoor exercise in the early morning hours within a few miles of the freeway and don’t keep your windows open at night.

What if You Currently Live by a Highway?

So what if you can’t avoid spending time near the freeway? If you have access to central air, install high efficiency air filters rated 13 or higher on the MERV scale (short for Minimum Efficiency Reporting Value) which quantifies how good the filters are at blocking out small pollution particles. Be sure to replace those filters every few months or as recommended by the manufacturer. If you don’t have central air, you can still purchase air-cleaning devices, but they need to be running all the time and usually only work for the one room that they are in.

Vegetation can reduce pollutants and carbon monoxide by as much as 60%.

Air filters also only work on certain pollutants. The US EPA provides a guide to different types of filters and their efficacy at blocking different forms of pollutants. Air filters are also only efficient when no other outside air can get inside. This means all windows and doors need to be closed and there can be no drafty doors or windows as are common in older homes. In the case of central air, the air must also be turned on and running.

Another way to lower the level of pollutants that reach your living space and thus your lungs is to live behind a sound wall, with thick trees or plants that extend above it. Vegetation along roadways can reduce pollutants in the form of ultrafine particles (UFPs) and carbon monoxide by as much as 60%.

Even if we live and work far from a highway, many of us still accumulate most of our exposure to traffic pollutants while commuting. If possible, spend less time in the car or opt for public transit methods that take you away from freeways. Otherwise, roll up your windows and recirculate the air in your car which can lower pollution levels inside your car as much as 80%.

Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com.

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