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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

Poster abstract for HEI Annual Conference 2022

Attendance 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, which can result in adverse health effects and missed days of school. To help 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. Despite this large investment, the effectiveness of this national program has yet to be evaluated.

Methods. We leveraged the randomized allocation of rebate funding to causally assess the impacts of the EPA’s 2012-2017 School Bus Rebate Programs on attendance rates. Using a classical causal framework for randomized controlled trials, we compare changes in school district level attendance rates after versus before each lottery year by funding selection status. In secondary analyses we examine heterogeneity of effect by quartiles of estimated ridership on applicant buses and by model years of the replaced buses.

Results. Of the total 3,153 EPA applicants, 2,816 had complete data and met our inclusion criteria; 383 of these applicants were selected for funding. The winning and losing districts were well balanced in terms of size, demographic make-up, and a proxy for socioeconomic status. Nationwide, districts selected for school bus rebate funding had, on average, a 0.06 percentage point (pp) higher attendance rate in the year after the lottery (95% confidence interval (CI): -0.01, 0.13) compared to districts not selected for funding. For an average size district of 10,000 students, this translates to approximately 6 additional students attending school each day in districts that won funding. The impacts of winning the lottery were even larger for districts with higher levels of ridership on the buses requested for replacement, with impacts of 0.14 pp (95% CI: -0.05, 0.32) for the highest estimated ridership group. Applicants that replaced pre-1990 and 1990-1999 model year buses had 0.43 pp (95% CI: 0.25, 0.61) and 0.10 pp (95% CI: -0.03, 0.22) improvements in attendance, respectively, compared to districts not selected for funding, whereas there was almost no improvement among the set of applicants that replaced model year 2000 and newer buses (-0.02 pp; 95% CI: -0.15, 0.10).

Conclusions. Overall, we find suggestive evidence that the EPA’s School Bus Rebate Program improved student attendance, especially in districts that removed the oldest buses and those with high levels of ridership on the applicant buses. Given the importance of attendance to educational success, our results suggest that in addition to the intended goals of increasing the pace at which older, highly polluting buses are removed from use, this program also has positive impacts on student attendance.