Harvard Study Indicates Health, Environmental Benefits of Electric School Buses

June 23, 2024

A row of Boston Public Schools electric buses.

Deploying one electric school bus in replacement of a diesel bus could result in up to $207,000 in climate and health benefits, according to a study released last month by Harvard researchers.

That figure accounts for replacing a 2005 model-year diesel school bus, which there are relatively few in active service, if in fleets at all. But one electric bus that replaces a 2017 model-year diesel bus could total $84,200 in total environmental benefits, concluded the paper submitted by the T.H. Chan School of Public Health to PNAS, the Proceedings of the National Academy of Sciences. Authors Ernani Choma, Kari Nadeau and Lisa Robinson compared carbon dioxide levels emitted from diesel tailpipes with electricity generation and battery production.

By replacing that same 2017 diesel bus, they found that $40,400 worth of climate benefits result from reduced greenhouse gas emissions in large cities, notably particulate matter (PM) 2.5. In less densely populated areas, the researchers noted that the climate benefits may be smaller. Meanwhile, health savings from replacing diesel with an electric bus totaled $43,800 by reducing air pollution, mortality rates and childhood asthma.

It noted that further research that assesses the benefits of reduced exposure of children to in-cabin air pollution “would be valuable to inform policy decisions.”

Diesel emissions have substantially improved since several studies in the early oughts looked at diesel exhaust levels inside school buses, including the Natural Resources Defense Council (2001), Environment and Human Health, Inc. (2002), and the California Air Resources Board (2003). A 2005 Clean Air Task Force study looked for the first time at the origins of the particulate matter emissions, and only the CARB study tested a retrofitted bus, and found that the front loading door was the predominant pathway that allowed the bus exhaust into the cabin, with the highest levels recorded at the front seats when the doors opened and on congested roadways as opposed to residential neighborhoods. The addition of a diesel particulate filter used with ultra-low sulfur diesel “effectively eliminated” school bus self-pollution in the cabin, though wind direction played a key role in additional exhaust emanating into the bus.

The paper published on May 20 is thought to be the first research of its kind to outline the health and environmental benefits of replacing older diesel school buses with electric school buses.

Until now, cost savings have focused on school district and bus company operations. In 2018, the Public Interest Research Group, or PIRG, published data that electric transit buses could save $2,000 in fuel and $4,000 in maintenance a year compared to diesel. Those numbers more than doubled to $5,000 and $10,000 for school buses in 2022, when clean energy advocate Advanced Energy United analyzed California Assembly Bill 2731, which it sponsored. The bill sought a zero-emissions requirement for all new school buses purchased starting in 2035.

AB 2731 ended up dying, but Assemblyman Phillip Ting resurrected it as AB 579 the following legislative session and it passed the legislature and was signed into law by Gov. Gavin Newsom.

In all, electric school buses could save $100,000 in lifetime fuel and maintenance, according to the World Resources Institute.

But that is with government subsidies, the Harvard study points out.

Still, the Harvard study noted that government subsidies such as the U.S. Environmental Protection Agency Clean School Bus Program is artificially affecting cost of ownership for electric buses. By removing subsidies, the authors write that TCO is $156,000 higher for an electric school bus compared to a diesel school bus. And they comment that previous estimates of $15,000 per year in V2G revenues for school districts are closer to $40 to $400 based on newer data.

“As electric buses are more costly, understanding their potential health and climate benefits is crucial to inform policy decisions regarding their adoption,” the report states.