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Assessing the national health and educational benefits of the EPA’s school bus retrofit and replacement program: A randomized controlled trial design

Principal Investigator: 

University of Michigan

This study will evaluate the National Clean Diesel Rebate Program, a lottery program that allocates available funding to school districts across the United States to replace or retrofit old-technology diesel powered school buses. Adar and colleagues will compare student health and educational performance in districts with and without such funding.

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Assessing National Health and Educational Benefits of the EPA’s School Bus Retrofit and Replacement Program: A Randomized Controlled Trial

Sara D Adar1, Richard Hirth1, Jennifer D’Souza1, Meredith Pedde1, Adam Szpiro2

1University of Michigan, Ann Arbor, MI, USA; 2University of Washington, Seattle, WA, USA

Background: Approximately 25 million children ride buses to school in the United States. During these commutes, children often breathe high levels of diesel exhaust putting them at greater risk of inflammation, poor lung function, and asthma attacks. Importantly, not all school buses have the same exposures to vehicle exhaust; newer buses with clean air technologies have lower in-cabin concentrations than older diesel buses. To help hasten the transition to cleaner vehicles, the Environmental Protection Agency (EPA) National Clean Diesel Rebate Program has provided approximately 28 million dollars in funding to public and private fleet owners to replace or retrofit old, highly polluting school buses since 2012. In spite of this large investment, the impacts of this national program on the health and educational attainment of students have not been evaluated.

Methods: We take advantage of the random allocation of funds under the National Clean Diesel Rebate Program between 2012 and 2017 to quantify the effects of funding for cleaner, upgraded buses on student attendance rates, emergency department visit rates for respiratory causes in the Medicaid population (5-18 years old), and standardized testing scores for math and English Language Arts. Using a classical causal framework for randomized controlled trials, we will compare changes in health and education between the year before and after the lottery for winning and losing districts. In secondary analyses, we will examine effect modification by the clean air technologies adopted, bus replacements versus retrofits, average age of the original buses, and lottery year as an indicator of changes in bus fleets over time. We will also examine differences by urbanicity since students in rural districts are more likely to have longer commutes and by school district socioeconomic position to indicate potentially sensitive subpopulations.

Results: Our previous testing of in-cabin air during nearly 600 trips in 200 Seattle school buses showed up to 50% reductions in particulate concentrations inside of diesel buses with the use of clean air technologies. In an intensive examination of 400 children, we have also shown that when children were riding newer, cleaner buses they were less likely to experience inflammation in their lungs and miss school than when they were riding older, dirtier school buses. Finally, pilot data from 999 school districts in the 2012 EPA lottery suggested a 1% greater improvement in attendance between the year after the lottery and the year before in districts that won EPA funds as compared to those districts that did not win funds.

Conclusions: We anticipate that this new accountability research will provide important insight into whether this ongoing program is having the intended results and impacts on school children’s health and educational performance. We further expect that our results will inform other clean vehicle programs.