Clean Diesel Bus Fleets

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What are clean diesel bus fleets?

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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 systemsexternal icon that help break down by-products of combustion or installing diesel particulate filtersexternal icon 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]

A group of illustrations of lungs, a doctor with a stethoscope, a dog, a dustmite, an inhaler, a building, a breathing machine (nebulizer), a nose with mucous dripping out of one nostril, a person coughing into their hand

CDC’s EXHALEpdf icon package includes evidence-based strategies to improve asthma control and reduce healthcare costs, including policy information about clean diesel bus fleets.

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.

  1. Beatty, T.K. and J.P. Shimshack, School buses, diesel emissions, and respiratory health. J Health Econ, 2011. 30(5): p. 987-99. doi: 10.1016/j.jhealeco.2011.05.017
  2. Diesel Technology Forum, Why Retrofit? Policy [cited 2016 June 1]; Available from: Why Retrofit?external icon.
  3. County Health Rankings & Roadmaps, Clean diesel technology fleet transition programs. 2014 September 3, 2014 [cited 2015 November 25]; Available from: Clean diesel technology fleet transition programsexternal icon.
  4. Texas Commission on Environmental Quality, Texas Emissions Reduction Plan (TERP) 2016 May 9, 2016 [cited 2016 June 1]; Available from: Texas Emissions Reduction Plan (TERP) external icon.
  5. State of New Jersey, Department of Environmental Protection, Bureau of Mobile Sources. NJDEP’s Mandatory Diesel Retrofit Program 2016 May 19, 2015 [cited 2016 June 1]; Available from: NJDEP’s Mandatory Diesel Retrofit Programexternal icon.
  6. U.S. Environmental Protection Agency, Learn About Clean Diesel. 2016 May 25, 2016 [cited 2016 June 1]; Available from: Learn About Clean Dieselexternal icon.
  7. Clean Air Task Force, C. Schneider, Editor,Diesel Emissions: Particulate Matter-Related Health Damages, 2004, Bethesda, MD. Available from: Diesel Emissions: Particulate Matter-Related Health Damagespdf iconexternal icon
  8. Steiner, S., et al., Diesel exhaust: current knowledge of adverse effects and underlying cellular mechanisms. Arch Toxicol, 2016. doi: 10.1007/s00204-016-1736-5
  9. Benbrahim-Tallaa, L., et al., Carcinogenicity of diesel-engine and gasoline-engine exhausts and some nitroarenes. The Lancet Oncology. 13(7): p. 663-664. doi:; 10.1016/S1470-2045(12)70280-2
  10. Adar, S.D., et al., Adopting clean fuels and technologies on school buses. Pollution and health impacts in children. American Journal of Respiratory and Critical Care Medicine, 2015. 191(12): p. 1413-1421.
  11. Brook, R.D., Cardiovascular effects of air pollution. Clin Sci (Lond), 2008. 115(6): p. 175-87. doi: 10.1042/CS20070444
  12. Brook, R.D., et al., Particulate matter air pollution and cardiovascular disease: An update to the scientific statement from the American Heart Association. Circulation, 2010. 121(21): p. 2331-78. doi: 10.1161/CIR.0b013e3181dbece1
  13. Pope, C.A., 3rd and D.W. Dockery, Health effects of fine particulate air pollution: lines that connect. J Air Waste Manag Assoc, 2006. 56(6): p. 709-42.

  14. Simkhovich, B.Z., M.T. Kleinman, and R.A. Kloner, Air pollution and cardiovascular injury epidemiology, toxicology, and mechanisms. J Am Coll Cardiol, 2008. 52(9): p. 719-26. doi: 10.1016/j.jacc.2008.05.029
  15. U.S. Environmental Protection Agency, Third Report to Congress: Highlights from the Diesel Emission Reduction Program. 2016, United States Environmental Protection Agency: epa.gov. Available from: Third Report to Congress: Highlights from the Diesel Emission Reduction Programexternal icon