Electric buses are only as clean as the grid that charges them. When it comes to greenhouse gas emissions, buses are already better than the competition. Buses charged by electricity are responsible for fewer carbon emissions than conventional diesel buses in any part of the U.S. electrical grid, a study by the Union of Concerned Scientists found. The research informs the ongoing debate over the future of bus procurement. As municipalities and transit agencies pursue cleaner buses, they have a few options other than diesel: natural-gas-powered, diesel-electric hybrid or full electric. Bus customers have to weigh several factors: upfront cost, total cost of ownership, tailpipe emissions, ability to get up hills and carbon emissions. Indeed, coal and gas plants remain major sources of greenhouse gas emissions. Critics of EV adoption efforts (or advocates for gas-powered buses) point to the grid mix and say that EVs aren’t so beneficial once the emissions from power production get factored in.

The UCS study paints a different picture of relative lifecycle greenhouse gas emissions. The researchers analyzed emissions from diesel- and natural-gas-powered buses — including the extraction, refining and delivery of the fuels, plus tailpipe emissions. For electricity emissions, they used Environmental Protection Agency power plant data from 2016, incorporating transmission losses and life cycle emissions from the fuels used in the plants. Across the vast majority of the nation, diesel buses would have to become at least twice as fuel-efficient to match the total greenhouse gas emissions of electric buses. The Northeast, Northwest and Mid-Atlantic perform the best. In upstate New York, for instance, the grid’s even split of hydropower, nuclear and natural gas yields an electric bus so clean that it equates to a diesel bus running at 37.3 miles per gallon. An actual diesel bus gets 4.8 miles per gallon, […]