Clean Diesel Bus Fleets

What are clean diesel bus fleets?

Diesel emissions can adversely affect health by contributing to poor air quality, and school buses and public transit buses are major producers of emissions.^[1] Transitioning fleets of buses to clean diesel technology involves retrofitting or modifying older diesel engines to run more cleanly.^[2] Retrofitting can include installing emission control devices such as closed crankcase ventilation systems that help break down by-products of combustion or installing diesel particulate filters to remove diesel soot (particulate matter) from the exhaust. The primary purpose of transitioning bus fleets is to reduce the amount of soot in the air from diesel emissions.^{[2, 3]}

Transitioning bus fleets can be implemented at the state or local level through a voluntary incentive or mandatory regulation.^[3] For example, the Texas Commission on Environmental Quality administers the Texas Emissions Reduction Plan (TERP), which provides financial incentives to local governments, businesses, and individuals to reduce emissions. ^[4] New Jersey requires owners of regulated vehicles, including school and commercial buses, to comply with a mandatory program enacted in 2005 under the Diesel Retrofit Law.^[5] Additional federal funding for the transition to clean diesel technology is available in the form of grants and rebates from the U.S. Environmental Protection Agency (EPA).^[6] Bus fleets targeted for retrofitting can include municipal or government buses, school buses, and privately maintained vehicles.^[3]

What is the public health issue?

According to the Clean Air Task force, adult exposure to diesel pollution contributes to 27,000 heart attacks, 14,500 hospitalizations and 2.4 million lost work days each year.^[7] Newer diesel engines operate more cleanly than in the past, but many older diesel engines that emit far more air pollution are still on the road.^[6] Diesel emissions contain numerous pollutants, including soot, nitrogen oxides, and carbon monoxide, that adversely affect cardiovascular and respiratory health.^[6] Evidence also shows that diesel exhaust is carcinogenic to humans, and it was classified as a Group 1 carcinogen by the International Agency for Research on Cancer in June 2012. ^{[8, 9]} Diesel soot from school buses has also been associated with reduced lung function and increased incidences of pneumonia in children. ^[10]

What is the evidence of health impact and cost effectiveness?

Retrofitting existing buses with clean diesel technology reduces air pollution, including soot, and can reduce diesel emissions by up to 85 percent.^[2] Evidence shows that reducing people’s exposure to soot can decrease the risk of mortality, heart attacks, and hospitalizations for heart disease.^[11-14] Vulnerable populations, like school children, can benefit from transitioning school bus fleets to clean diesel technology. Clean diesel school bus fleets have been shown to reduce the amount of air pollution that school children are exposed to, improve lung function, and reduce hospitalizations due to pneumonia.^{[1, 10]} One study in the Puget Sound region of Washington showed that school districts that installed any type of clean diesel retrofit technology in their school buses experienced a 23 percent decrease in the number of pediatric bronchitis and asthma cases and 37 percent fewer pediatric pneumonia cases per month. Districts that specifically adopted crankcase ventilation filter installations experienced a 33 percent drop in pediatric bronchitis and asthma cases.^[1]

According to the EPA, each federal dollar invested in clean diesel projects has generated between $5 to $21 in savings from public health benefits.^[15] The EPA estimates that the lifetime value of health benefits of engines retrofitted or replaced through Diesel Emission Reduction Act (DERA) grants from 2009 to 2013 totaled $11 billion dollars. This includes the value of up to 1,700 premature deaths averted due to emissions reductions.^[15]

For questions or additional information, email healthpolicynews@cdc.gov.