Electric school bus carbon test: Why the EPA’s new green-school grants matter

Harvard scientists find American cities save $207,200 every time they electrify just one old diesel bus

By Rae Hodge

Staff Reporter

Published May 23, 2024 6:01AM (EDT)

School Bus (Getty Images/shaunl)
School Bus (Getty Images/shaunl)

There are currently more than half a million diesel school buses rumbling and coughing along America's roadways in 2024, carrying around 24 million students to public and private schools alike. The EPA estimates that about 40% of that fleet is now more than 11 years old, which is the driving reason behind the agency's Clean School Bus Program, with $5 billion in funding through the Bipartisan Infrastructure Law. On Monday, a trio of Harvard health and environmental scientists found that school districts would save an average of $247,600 in costs for every one of the roughly 200,000 high-emission heavy duty vehicles they replace with an electric bus

 In an analysis published in the Proceedings of the National Academy of Sciences, researchers from Harvard's T.H. Chan School of Public Health found that lowering the number of emissions-driven deaths and childhood asthma cases — not to mention reducing negative climate impacts — by replacing old diesel buses with new electric ones via EPA funding would save about "$207,200 per bus and $40,400 per bus, respectively." The totals accounted for a vehicle benefit of $84,200 per bus, $43,800 in health benefits and $40,400 in climate benefits. The study's authors found that if the entire fleet of U.S. school buses had been replaced in 2017 with EVs, emissions-related deaths would have been reduced by around 24 times, and new childhood asthma cases would have been reduced by around 23-fold.

"The transportation sector is the largest contributor to U.S. greenhouse-gas emissions. Vehicle emissions are also an important contributor to ambient air pollution, causing substantial health effects," wrote the study's authors. "Several recent studies have attributed roughly 20,000 deaths per year in the United States to vehicle emissions, despite recent decreases. Around 90% of this mortality burden is due to exposure to ambient fine particulate matter, with ozone representing the remaining 10%." 

Chronic exposure to ambient particular matter, or PM2.5, is causing a surge in mortality among adults and asthma in kids, with some U.S. areas seeing acute impacts about 10 times worse those measured in severe-haze urban areas in China. Researchers said that, among the U.S. 20,000 annual deaths, PM2.5 "is the environmental exposure responsible for the largest mortality burden in the United States. PM2.5 is emitted directly from vehicles (primary PM2.5) or is formed in the atmosphere after vehicle emissions of precursor gases."  

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The EPA's Clean Bus Program currently has only a five-year funding window for its $5 billion carveout, which ends in 2026. That could prove to be a challenging timeline as districts continue to face an ongoing national shortage of bus drivers. The agency does grant priority, however, to districts more likely to be struggling, meaning those still using buses manufactured in 2010 or earlier. Using EPA funds to replace the aging fleet with cleaner and healthier zero- or low-emission buses could offer critically needed budget savings by alleviating health costs.

Researchers note that the $5 billion in funding can only replace only around 15,000 buses, however, which is just 3% of the 200,000 heavy-pollution diesel buses. And replacing the entire diesel bus fleet won't come cheap. The study's authors found that, without significant subsidies, per-vehicle ownership and upkeep cost for an electric bus is about $156,000 more than that for buying and maintaining a new diesel. Replacing 200,000 buses with another round of health-hazardous diesels would cost between $60 billion to $80 billion; after accounting for rollout costs, full electric replacement would cost about 2.5 times as much.

It's unquestionably a painful calculus: With the need for greater funding in the coming years, lawmakers in Congress deliberating EPA funding will have to weigh those costs against the rising tide of political campaign contributions from the fossil fuel lobby, with the health of millions of children potentially hanging in the balance.  

By Rae Hodge

Rae Hodge is a science reporter for Salon. Her data-driven, investigative coverage spans more than a decade, including prior roles with CNET, the AP, NPR, the BBC and others. She can be found on Mastodon at