Clean diesel technology fleet transition programs

Clean diesel technology transition programs replace or retrofit government or privately operated diesel vehicles (e.g., buses) until the entire fleet operates with clean diesel technology. Vehicles are often replaced towards the end of their useful life. Diesel powered engines can be retrofitted with control devices such as diesel particulate filters (DPF), diesel oxidation catalysts (DOC), and closed crankcase ventilation systems (CCV). Diesel exhaust is carcinogenic, and contains numerous pollutants that negatively affect cardiovascular and respiratory health; estimates suggest exposure contributes to 27,000 heart attacks, 14,500 hospitalizations, and 2.4 million lost work days each year (CDC-Clean diesel).

Expected Beneficial Outcomes (Rated)

  • Reduced emissions

  • Improved air quality

Other Potential Beneficial Outcomes

  • Improved health outcomes

Evidence of Effectiveness

There is strong evidence that adopting clean diesel technology through diesel transition programs decreases environmental exhaust emissions (US EPA-Transportation 2006Barone 2010, Sandhu 2015). Retrofitting diesel buses has also been shown to improve in-cabin air quality by decreasing particulate matter, organic carbon, and elemental carbon in some circumstances (Barone 2010).

Decreases in emissions associated with retrofitted diesel buses appear to have positive effects on riders’ health. A Washington-based study, for example, indicates reductions in bronchitis, asthma, and pneumonia among children in school districts with retrofitted buses (), as well as improvements in lung function and reductions in absenteeism, especially among children with asthma (Adar 2015). Retrofitting may also decrease the costs associated with respiratory disease-related hospitalizations and treatment ().

Costs for diesel retrofit devices vary based on the manufacturer, labor requirements, and type of technology. For example, a diesel particulate filter typically costs $5,000-$15,000, but can cost up to $50,000 for some large equipment. A diesel oxidation catalyst typically costs $600-$2,000 or more (US EPA-Diesel technologies). A Washington-based cost-benefit analysis indicates that school bus retrofitting has positive net benefits (). The US EPA estimates that every federal dollar invested in clean diesel retrofits or replacements generates between $5 and $21 in savings from improvements in public health (CDC-Clean diesel).

Vehicle replacement is suggested instead of retrofitting for vehicles nearing the end of their useful life; replacement improves vehicle safety, reliability, and fuel efficiency, and reduces maintenance costs and emissions (US EPA-CD and DERA).

Impact on Disparities

No impact on disparities likely

Implementation Examples

Many states have mandatory or voluntary programs to support diesel retrofit efforts, as in California, Illinois, New Jersey, Oregon, and Texas (IL EPA-Green fleetsOR DEQ-DieselDiesel Forum-Retrofit). Chicago and New York City are examples of municipalities that provide incentives and support to retrofit or replace diesel vehicles (CDOT-DCCDiesel Forum-Retrofit).

The US Department of Transportation Federal Highway Administration’s Congestion Mitigation and Air Quality Improvement (CMAQ) Program funds efforts to improve air quality, including diesel engine retrofits (US DOT-CMAQ). The US Environmental Protection Agency (US EPA) manages funds appropriated for the Diesel Emission Reduction Act (DERA) to retrofit older diesel vehicles. In 2014, Congress appropriated $20 million for DERA retrofit activities (Diesel Forum-Retrofit, US EPA-CD and DERA). The proposed budget for FY 2016 also includes grant funding for the DERA program, as well as additional funds to retrofit, replace or repower diesel equipment, especially school buses (NACAA-Appropriations). 

Implementation Resources

US EPA-CD and DERA - US Environmental Protection Agency (US EPA). Clean diesel and DERA funding.

US EPA-Clean school bus program - US Environmental Protection Agency (US EPA). Clean school bus program.

Diesel Forum-Retrofit - Diesel Technology Forum. Retrofit: Why retrofit?

US EPA-Clean diesel - US Environmental Protection Agency (US EPA). Learn about clean diesel: Impacts of diesel emissions, Diesel Emissions Reduction Act (DERA), and other federal funding.

Citations - Evidence

* Journal subscription may be required for access.

Borak 2007* - Borak J, Srianni G. Studies of self-pollution in diesel school buses: Methodological issues. Journal of Occupational and Environmental Hygiene. 2007;4(9):660-8.

Barone 2010 - Barone TL, Storey JME, Domingo N. An analysis of field-aged diesel particulate filter performance: Particle emissions before, during, and after regeneration. Journal of the Air & Waste Management Association. 2010;60(8):968-76.

Beatty 2011* - Beatty TKM, Shimshack JP. School buses, diesel emissions, and respiratory health. Journal of Health Economics. 2011;30(5):987-99.

US EPA-Transportation 2006 - US Environmental Protection Agency (US EPA). Diesel retrofit technology: An analysis of the cost-effectiveness of reducing particulate matter emissions from heavy-duty diesel engines through retrofits. 2006.

Trenbath 2009* - Trenbath K, Hannigan MP, Milford JB. Evaluation of retrofit crankcase ventilation controls and diesel oxidation catalysts for reducing air pollution in school buses. Atmospheric Environment. 2009;43(37):5916-22.

Zhang 2011* - Zhang Q, Zhu Y. Performance of school bus retrofit systems: Ultrafine particles and other vehicular pollutants. Environmental Science & Technology. 2011;45(15):6475-82.

US EPA-CD and DERA - US Environmental Protection Agency (US EPA). Clean diesel and DERA funding.

US EPA-Diesel technologies - US Environmental Protection Agency (US EPA). Clean diesel: EPA-verified retrofit technologies that save fuel and reduce emissions and can be used for all diesel engines.

Sandhu 2015 - Sandhu GS, Frey HC, Bartelt-Hunt S, Jones E. In-use activity, fuel use, and emissions of heavy-duty diesel roll-off refuse trucks. Journal of the Air & Waste Management Association. 2015;65(3):306-323.

Adar 2015 - Adar SD, D’Souza J, Sheppard L, 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):1413–1421.

CDC-Clean diesel - Centers for Disease Control and Prevention (CDC), Office of the Associate Director for Policy. Clean diesel bus fleets. Health impact in 5 years (HI-5): Transitioning bus fleets, cleaner air for a healthier community.

Citations - Implementation Examples

* Journal subscription may be required for access.

US EPA-CD and DERA - US Environmental Protection Agency (US EPA). Clean diesel and DERA funding.

US DOT-CMAQ - US Department of Transportation (US DOT). Congestion mitigation and air quality improvement (CMAQ) program.

Diesel Forum-Retrofit - Diesel Technology Forum. Retrofit: Why retrofit?

CDOT-DCC - Chicago Department of Transportation (CDOT). Drive Clean Chicago (DCC) program and the Drive Clean Truck-Voucher program.

OR DEQ-Diesel - Oregon Department of Environmental Quality (OR DEQ). Air quality: Clean diesel success stories including Oregon's Clean Diesel Initiative.

IL EPA-Green fleets - Illinois Environmental Protection Agency (IL EPA). Illinois Green Fleets Program: Green environment, green energy, and green economics for a green Illinois.

NACAA-Appropriations - National Association of Clean Air Agencies (NACAA). FY 2017 budget and congressional appropriations.

Date Last Updated

Feb 27, 2017