A new study by UNM Assistant Professor of Civil Engineering Gregory Rowangould shows 19 percent of the population of the United States, or nearly 60 million people, live in close proximity to high volume roads.  While prior research documents higher concentrations of many air pollutants found in vehicle exhaust along roads with heavy traffic and higher rates of many diseases including cancer, respiratory illness and heart disease, there was little information about how many people actually live in those areas and who they are. 

In addition to finding a surprisingly large portion of the U.S. living very close to heavily trafficked roads, the study also finds that people living closer to roads with higher traffic volumes are more likely to belong to a minority population or have lower incomes than residents living further away, and that in most counties there are no air quality monitors to measure pollution levels near roadways.

Rowangould took average annual daily traffic volume data for 2008 from the highway performance monitoring system road network in the 2010 National Transportation Atlas Database.  He combined that information with the 2010 U.S. Census block level population counts and block-group level median household income data from the 2000 Census to reach his results.  The study can be found here.

The study shows that on average, California has the greatest proportion of residents living near high volume roads, at nearly 40 percent of its population.  While that may not be a surprise for those that have visited Southern California or the Bay Area, the study finds similar proportions in many other regions.

For example, the study finds that in New Mexico 38 percent of Bernalillo County’s population, or more than 250,000 people, live within 500 meters of roads with more than 25,000 vehicle trips per day.  More than 16 percent of New Mexico’s population lives near these heavily trafficked roads where exposure to vehicle emissions may be higher.  These findings reveal that public health concerns over vehicle emissions exposure are not limited to the largest cities that have received most of the attention in the past, but that health risks may be very widespread.

The study also revealed that environmental justice concerns are also widespread and very common.  More than 80 percent of counties in the U.S. have a disproportionally large number of their minority and low income residents living near the most heavily trafficked roads.

Rowangould also looked at where communities place their regulatory air quality monitors required by the Clean Air Act.  He finds that few monitors are placed within close proximity to roads.  He says that is significant because a violation of National Ambient Air Quality Standards (NAAQS) recorded by one of those air quality monitors would require communities to reduce emissions from mobile sources and perform more detailed air quality analysis when developing transportation plans.

Rowangould says “The absence of air quality monitors along high volume roads where people live may prevent communities from detecting violation of air quality standards and health risks.”  He cautions that his analysis considers populations that may be at risk based only on a measure of their proximity to high volume roads, but that actual pollution levers and risk depend on many factors, including the type of vehicles and fuels used, local weather patterns, where people spend most of their time, and the terrain along the roads.  With that said, he notes that some recent studies have shown that high concentrations of air pollutants from vehicle emissions can reach well beyond the 500 meter limit considered in his study.

He is now developing new planning models to help transportation planners and highway engineers predict the air quality impacts of transportation decisions so that additional exposure can be avoided and existing exposure can be reduced.  The new modeling tools will also shed new light on environmental justice concerns by identifying populations and communities facing disproportionally high exposure to vehicle emissions.