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Assessing 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.

Funded under
In review

Poster abstract for HEI Annual Conference 2023

Benefits of the EPA’s School Bus Rebate Program: A Randomized Design

Meredith Pedde1, Adam Szpiro2, Richard Hirth1Sara D Adar1

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. While school buses remain the safest school transport from a traffic accident perspective, older buses can expose students to high levels of diesel exhaust. These exposures can adversely impact health, which might cause missed school days and reduced learning. To hasten the transition to cleaner vehicles, the Environmental Protection Agency’s (EPA’S) ongoing School Bus Rebate Program randomly allocated almost $28 million to replace older, more polluting school buses with cleaner alternatives between 2012 and 2017. The effectiveness of this national program has yet to be evaluated.

Methods. Leveraging the randomized allocation of rebate funding, we assessed the impacts of the EPA’s 2012-2017 School Bus Rebate Programs on attendance, educational achievement, emergency department visits for respiratory causes among children in Medicaid, and community air pollution levels. Using a classical causal framework for randomized controlled trials, we compared changes in school district levels of each outcome after versus before each lottery year by funding selection status. In secondary analyses we examined the heterogeneity of effects by model years of the replaced buses and quartiles of estimated ridership on applicant buses.

Results. Of the 3,153 applicants, 430 were randomly selected for funding. These districts were similar in terms of size, demographic make-up, and a proxy for socioeconomic status to districts not selected for funding. Selected districts had, on average, a 0.06 percentage point (pp) increase in attendance rate (95% confidence interval (CI): -0.01, 0.13), 0.01 standard deviation (SD) increase in reading and language arts (RLA) test scores (95% CI: -0.01, 0.02), and 0.3 µg/m3 reduction in average PM2.5 concentrations (95% CI: -0.5, -0.1) in the year after the lottery compared to districts not selected for funding. We observed no improvements in math scores or hospitalization rates for districts selected for funding. Applicants that replaced pre-1990 model year buses had the largest gains with 0.43 pp (95% CI: 0.25, 0.61) higher attendance, 0.06 SD higher RLA test scores (95% CI: 0.05, 0.08), 0.03 SD higher math test scores (95% CI: 0.01, 0.04), and 1.2 µg/m3 (95% CI: -2.2, -0.2) lower average PM2.5 compared to districts not selected for funding; the replacement of model year 2000 and newer buses showed almost no impact. Observed impacts were also larger for districts with more replaced buses and greater estimated ridership on those buses.

Conclusions. We find evidence that the EPA’s School Bus Rebate Program improved student attendance, educational performance, and air quality though we found no impacts on emergency department visits among children in Medicaid. Results were most robust for replacement of pre-1990 buses and districts with high levels of ridership. Our results suggest that by increasing the pace at which older, highly polluting buses are removed from use, this program positively impacts student attendance, educational achievement, and ambient air quality.