Science: Health Risk Zones

Over the last ten years, there has been an accumulation of public health studies showing that air pollution exposure levels are greater close to roadways than are typically reported through regional air pollution measurements. There will always be some variability, because traffic pollution is affected by the mix of vehicles on a roadway, wind and weather, topography, and the buildings around the roads. Congestion itself has an effect: Stop-and-go traffic releases as much as three times the pollution of free-flowing traffic. 

Dr. Ying Zhou and Dr. Jonathan Levy, researchers at the Harvard School of Public Health (HSPH), recently synthesized much of the related research from the last decade. They concluded that there is a zone of increased exposures surrounding major roadways, i.e. an area in which increased health risks would be expected.

The synthesis was based on 30 peer-reviewed studies and three government regulatory reports that characterized how air pollution levels and health risks changed with distance from a roadway. It identified the factors that would potentially influence the findings, including distance from the road, type of pollutant, emission rates, background pollution concentrations, and meteorological conditions.

Zhou and Levy concluded that the size of the area around the road where pollution levels were noticeably higher varied by pollutant. For the following three traffic-related pollutants known to cause health problems, they summarized the distance from the road where levels are high enough to increase health risks.

• Particulate matter (soot from gasoline or diesel): 500 to 1500 feet
• Nitrogen dioxide (NO2): 600 to 1500 feet
• Ultrafine particle count (the smallest soot particles): 300 to 1000 feet

Taking all the different traffic-related pollutants as a whole, a risk zone of 500 to 1500 feet around a major roadway is supported by this meta-study.

Posted: 17-Sep-2008; Updated: 30-Oct-2008