Near Roadway Air Pollution and
Health: Frequently Asked Questions
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People who live, work or attend school near major roads appear to have an increased incidence
and severity of health problems that may be related to air pollution from roadway traffic. Health
effects that have been associated with proximity to roads include asthma onset and aggravation,
cardiovascular disease, reduced lung function, impaired lung development in children, pre-term
and low-birthweight infants, childhood leukemia, and premature death. Other than air pollu-
tion, road noise may also play a role in the health problems associated with roadway exposure.
What is a "major road" and how close to a such a road do you have to live, work or attend
school to be considered "near" it?
Research findings indicate that roadways generally influence air quality within a few hundred
meters - about 500-600 feet downwind from the vicinity of heavily traveled roadways or along
corridors with significant trucking traffic or rail activities. This distance will vary by location
and time of day or year, prevailing meteorology, topography, nearby land use, traffic patterns, as
well as the individual pollutant.
What influences air quality near major roadways?
The type of vehicles and fuel used, traffic activity, and the wind speed and direction can all have
big effects on pollutant levels near major roadways. Generally, the more traffic, the higher the
emissions; however, certain activities like congestion, stop-and-go movement or high-speed
operations can increase emissions of certain pollutants. The combination of rush hour and calm
winds in the morning often leads to the highest concentrations during this time of the day.
Emissions can be elevated near major roadways and arise from multiple vehicle-related pro-
cesses, including tailpipe exhaust, evaporation of fuel, brake and tire wear, and dust kicked up
from traffic. Certain wind and terrain conditions, certain times of the day, including rush hours
can result in elevated concentrations of air pollution near the road and air pollutants traveling
farther from the road. The presence of sound walls, buildings and vegetation also has an impact
on pollutant dispersion. Typically, pollutant concentrations decrease with distance away from
traffic although the degree of this decrease varies.
•	The highest concentrations of roadway pollutants occur on or just downwind of a road-
way. With greater distance from a roadway, concentrations generally decrease to back-
ground levels within 500-600 feet. Pollutant concentrations tend to be higher when
winds blow from the road and wind speeds are low.
•	Traffic activity, wind speed, and direction can have a big influence on pollutant concen-
trations. Generally, the more traffic, the higher the emissions; however, certain activities
like congestion, stop-and-go movement or high-speed operations can increase emissions
of certain pollutants. The combination of rush hour and calm winds in the morning
often leads to the highest concentrations during this time of the day. Other factors af-
fecting pollutant concentrations include the mix of vehicles, roadway design, and nearby
land uses.
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Both heavy-duty trucks and light-duty gasoline vehicles emit a range of pollutants. However,
their contributions to different types of compounds are not the same. Per vehicle, heavy-duty
diesel trucks can emit more of certain pollutants (e.g., NOx and PM) and contribute dispropor-
tionately to the emissions from all motor vehicles. Gasoline-powered passenger cars generally
emit more of other pollutants (e.g., CO, and benzene, a volatile organic compound (VOC)).
How many people live or spend time near major roads and other transportation facilities?
EPA estimated that in 2009, more than 45 million people in the United States lived within 300
feet of a highway with 4 or more lanes, a railroad, or an airport, and population trends suggest
this number is increasing. Many schools and child care centers are located within a few hundred
feet of highways, particularly in urban areas. Furthermore, every day, the average American
spends more than an hour in travel, most of which takes place on major roadways
Are some people at greater risk from being close to major roadways or high traffic areas?
Children, older adults, people with preexisting cardiopulmonary disease, and people of low
socioeconomic status are among those at higher risk for health impacts from air pollution near
roadways.
Some people are known to be at greater risk of experiencing adverse health effects from air pol-
lution, including those with asthma and other respiratory diseases and risk factors for heart at-
tacks and strokes. Children, older adults, people with preexisting cardiopulmonary disease, and
people of low socioeconomic status also are among those at higher risk for health impacts from
some air pollutants associated with traffic emissions.
There are many factors being studied to better determine personal risk from air pollution gener-
ated from traffic. These include a person's current health status and age and the frequency and
amount of exposure to air pollutants. EPA scientists and scientists funded through EPA grants
continue to study the association between roadway air pollutants and potential health impacts.
Studies are examining the role of traffic-related air pollutants on the initiation of asthma and
other diseases in children and cardiovascular disease in adults.
What is EPA doing to address near-roadway air pollution?
Over the past three decades the U.S. EPA has worked to reduce harmful roadway-related emis-
sions in a number of important ways. EPA has reduced pollution from new cars and trucks by
establishing more stringent emission standards and cleaner fuel requirements. EPA also has a
number of programs designed to reduce emissions from in-use vehicles not subject to the newest
emission standards. In addition, EPA sets the health-based National Ambient Air Quality
Standards (NAAQS) for pollutants that are emitted from on-road mobile sources and has
recently required that air quality monitors be placed near high-traffic roadways for determining
compliance with the NAAQS for N02, CO, and PM2.5. Finally, EPA is conducting research to
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•	What can be done to reduce exposures near roadways to maximize improvements in
public health?
•	How can research support the improvement of existing tools and development of new
tools for use in transportation and community planning?
•	How can research help inform regulatory decisions to improve near-road air quality and
reduce occurrences of adverse health effects?
Research includes:
•	Health effect studies of human populations in neighborhoods near major roads
•	Toxicological and human clinical studies in controlled exposure environments
•	Air monitoring studies on and near roadways
•	Laboratory studies to measure motor vehicle emissions and simulate roadway conditions
•	Computer modeling to understand air quality and the dispersion of pollutants away from
the roadway
•	Field and laboratory studies on the ways to reduce near-road air pollutants and adverse
health effects and
•	Impacts of ports, railyards, and airports on nearby air quality and people's exposures.
For more information, see:
www.epa.gov/air-research/research-near-roadway-and-other-near-source-air-pollution
What has been the impact of near-roadway research?
Near-roadway research has led to a number of programs aimed at reducing pollutant concen-
trations and protecting public health. The research contributed to a body of evidence on the
connections between roadway-associated exposures and adverse health effects, which led EPA to
develop the requirement for a national near-road air quality monitoring network and supported
EPA programs for modeling the near-road air quality impacts of diesel vehicles on transportation
projects. In particular, the health studies helped to identify health impacts near roads, the field
measurements identified where and how best to monitor these impacts, and the field and labora-
tory studies suggested ways to potentially model and mitigate these impacts.
Communities have used products of this research to inform decisions on school and other
facility placement. For example, research studies were cited in the recent EPA School Siting
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Guidelines, which help school districts evaluate potential environmental hazards when identify-
ing new school locations, and identify roadway-related factors and mitigation options that may
reduce exposures. For recommendations on addressing near-road air quality in school siting, see
section 8 in EPA's School Siting Guidlines:
www.epa.gov/schools/guidelinestools/siting/download.html
This research has also led community planners and developers to consider how people may be
exposed to traffic emissions, and what steps may be taken to reduce nearby populations' expo-
sures and health impacts.
Where can I find published research?
•	To find specific publications related to near roadway research, enter "roadway" or "road"
in the search box on the main page of the Science Inventory at: http://cfpub.epa.gov/si/.
•	EPA's near roadway research:
www.epa.gov/air-research/research-near-roadway-and-other-near-source-air-pollution
•	EPA also supports near roadway research conducted at other research institutions includ-
ing the EPA Clean Air Research Centers and the Health Effects Institute (HEI). Infor-
mation on near roadway research at these institutions can be found at the following sites:
o Clean Air Research Centers:
www.epa.gov/air-research/air-climate-and-energy-ace-centers-supporting-air-quality-
and-climate-solutions-0
o Health Effects Institute: www.healtheffects.org/
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