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Cleaner Air

two people riding bikes along a river's edge on a bike path

Photo credit: / Laura Sandt

Relationship to public health

Motor vehicles are a leading source of air pollutants that affect human health. Vehicle emissions contribute to the formation of ground level ozone (smog), which can trigger health problems such as aggravated asthma, reduced lung capacity, and increased susceptibility to respiratory illnesses, including pneumonia and bronchitis. Motor vehicles, particularly those used for freight, are also a major source of fine particulate matter.

Many scientific studies have linked breathing particulate matter to significant health problems, including asthma, chronic bronchitis, and heart attacks. Diesel particulate matter is of particular concern because long-term exposure is likely to cause lung cancer. Levels of traffic-related air pollution are higher near major roadways that have high traffic volume.

Transportation agencies and local jurisdictions can reduce traffic-related air pollution and improve air quality in five ways:

  1. Develop cleaner travel options through measures such as expanding public transportation systems, improving public transportation service, and developing or improving bicycling and pedestrian infrastructure.
  2. Reduce the distance between key destinations required to satisfy daily needs through more efficient land use planning and zoning, making it more attractive and convenient to walk or bicycle instead of using motor vehicles for transportation.
  3. Create or support clean fueling infrastructure, such as electric vehicle charging and hydrogen fueling stations.
  4. Manage the transportation system to increase vehicle and system operating efficiency through measures such as anti-idling policies, improved incident response, real-time travel information for public transportation, and congestion management.
  5. Buy green fleet vehicles and equipment, including equipment with increased fuel efficiency, hybrid electric vehicles, and equipment that runs on clean fuels.

The Transportation and Health Tool focuses on measures to improve air quality by developing cleaner travel options.

Related indicators in the THT

Commute mode share describes the percentage of workers who commute by public transportation, bicycle, or foot, all of which pollute less than driving.

Miles traveled by mode describes the relative distance that people travel using modes that produce less pollution than driving.

Vehicle miles traveled (VMT) per capita provides a measure of how much the average person drives. As VMT per capita fall, so do pollutant emissions from passenger vehicles.

Proximity to major roadways describes the proportion of the population of a metropolitan area or state that lives within 200 meters of a roadway that has at least 125,000 annual average daily traffic (AADT). That represents the population with increased exposure to concentrations of traffic-related air pollution.

Public transportation trips per capita describes how often people ride public transportation, which produces fewer emissions than driving.


Environmental Protection Agency's Air Quality Trends

The Environmental Protection Agency (EPA) provides current and historic data on air quality trends for the pollutants regulated by the agency, including modeled air quality data and data from local ambient air quality monitors. Information is also available on sources, health effects, and programs to reduce individual pollutants.

Environmental Protection Agency Guidance on Improving Air Quality through Land Use Activities

This EPA guidance presents the conditions under which the benefits of land use activities could be included in air quality and transportation planning processes. Land use activities are a tool to encourage the development of land use policies and projects that improve livability in general, and air quality in particular.

Alternative Fuels Data Center

The U.S. Department of Energy's Alternative Fuels Data Center provides information on using biodiesel, electricity, ethanol, hydrogen, natural gas, and propane to fuel vehicles. For each fuel, the site provides information on benefits and considerations, vehicles that use the fuel, and laws and incentives that support increased use of the fuel. The site also contains maps to help users locate alternative fueling stations.

National Environmental Public Health Tracking Network

CDC’s National Environmental Public Health Tracking Network provides a variety of state- and county-level health data, including summaries of EPA air quality data on particulate matter and ozone levels.

Environmental Protection Agency’s Resources for State and Local Governments

EPA’s Office of Transportation and Air Quality provides guidance, tools, and information on funding sources to help state and local governments improve air quality.

Federal Highway Administration’s Air Quality Site

The Federal Highway Administration provides information on how air pollutants are regulated through federal transportation planning and funding processes, and information on funding sources available for projects that improve air quality.

Research Studies

Traffic-Related Air Pollution: A Critical Review of the Literature on Emissions, Exposure, and Health Effects

This comprehensive review describes the available research investigating the link between exposure to vehicle pollution and several different health outcomes, including cardiovascular health, lung function, and birth outcomes.

Health Effects Institute. 2010. Traffic-related air pollution: a critical review of the literature on emissions, exposure, and health effects.

Potential Health Effects Associated with Residential Proximity to Freeways and Primary Roads: Review of Scientific Literature, 1999-2006

The authors provide a comprehensive review of literature on the health effects of living near high traffic volume roadways.

Boothe VL, Shendell DG. Potential health effects associated with residential proximity to freeways and primary roads: review of scientific literature, 1999-2006. Journal of Environmental Health 2008;70:33-41;55-56.

Conserving Energy and Preserving the Environment: The Role of Public Transportation

This report compares the air pollution impacts of public transportation and passenger vehicles on a per passenger mile basis.

Shapiro RJ, Hassett KA, Arnold FS. Conserving energy and preserving the environment: the role of public transportation. American Public Transportation Association; 2002.

Fine-Particulate Air Pollution and Life Expectancy in the United States

This report estimates the impact of reducing particulate pollution on life expectancy using data from U.S. counties and metropolitan areas.

Pope CA, Ezzati M, Dockery D. Fine-particulate air pollution and life expectancy in the United States. New England Journal of Medicine 2009;360(4):376-386.

Effects on Respiratory Health of a Reduction in Air Pollution from Vehicle Exhaust Emissions

The authors examine the effects of vehicle exhaust on people who live near roadways. They compare pollution concentrations and respiratory surveys in a neighborhood before and after construction of a bypass intended to reduce congestion.

Burr ML, Karani G, Davies B, Holmes BA, Williams KL. Effects on respiratory health of a reduction in air pollution from vehicle exhaust emissions. Occupational and Environmental Medicine 2004;61(3):212-218.

A Census of the US Near-Roadway Population: Public Health and Environmental Justice Considerations

This report examines the population, location, and demographic characteristics of communities living near high traffic volume roadways.

Rowangould G. A census of the US near-roadway population: public health and environmental justice considerations. Transportation Research Part D: Transport and Environment 2013;25:59-67.