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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

Assessing National Health and Educational Benefits of the EPA’s School Bus Retrofit and Replacement Program: A Randomized Controlled Trial 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 school buses each day in the United States (US). While school buses remain the safest school transport from a traffic accident perspective, the use of older school buses often means high student exposures to diesel exhaust. With school bus in-cabin pollutant exposures reaching levels up to ten times that in ambient air, even relatively short commutes on dirty school buses can contribute a disproportionately high fraction to students’ daily air pollution exposures. This raises concerns given the adverse health effects associated with traffic-related pollutants, which can lead to missed school days for students. To hasten the transition to cleaner vehicles, the US Environmental Protection Agency (EPA) awards funds using a random lottery approach to fleet owners for the replacement or retrofit of old, highly polluting school buses under the National Clean Diesel Rebate Program. The EPA has awarded almost $28 million for clean school buses since the still-running program began in 2012. However, the effectiveness of this program has yet to be evaluated. In this project we take advantage of the randomized funding allocation for school bus replacements and retrofits to assess the impacts of the 2012-2017 EPA school bus replacement and retrofit programs 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.

Methods. Using lottery entrant information from the EPA and attendance data from state Departments of Education, we evaluated whether districts awarded EPA funding saw greater improvements in student attendance after their school bus replacements as compared to districts who were not awarded funding. We performed a classical intent-to-treat analysis for randomized control trials with additional adjustments for district attendance rates in the year before the lottery, lottery year, urbanicity, region, and number of applications entered for a district. We fit these models using general estimating equations with robust standard errors clustered at the state level. In secondary analyses we evaluated effect modification of the impacts of winning the lottery by school bus ridership levels, which we estimated using the number of buses funding was requested for and US Department of Education school district enrollment data.

Results. Preliminary findings based on our successful linkage of attendance data to nearly 90% of the applicants suggested that being selected to receive EPA clean bus funding was associated with a 0.05 percentage point increase (95% CI: -0.02, 0.13) in attendance in the school year after compared to before the funding lottery. For a school district with 10,000 children, this would translate to 5 additional children attending school each day. Notably, the magnitude of this association increased with increasing fractions of students in the district that were likely to ride buses replaced with EPA funds.

Conclusions. Preliminary work shows a promising impact of the EPA’s clean bus funding program on student attendance. Further work will finalize these models with all available data and assess the program’s impact on educational achievement and emergency department visit rates for respiratory causes in the school-aged Medicaid population.