The transportation sector accounts for 27 percent of US greenhouse gas (GHG) emissions, more than any other sector of the economy. Passenger cars and light trucks emit most of the transportation sector’s GHGs, and they are also major contributors to local air quality problems; at least 125 million US residents live in areas that violate air quality standards.1 Public and media attention has focused on the potential for plug-in electric vehicles (PEVs), which include electric vehicles like the Tesla Model 3 and plug-in hybrids like the Chevrolet Volt, to substantially reduce pollution from passenger vehicles. PEV subsidies in the 2022 Inflation Reduction Act are intended to help achieve the Biden administration’s GHG emissions goals. The Biden administration and many states have set economy-wide GHG emissions targets for the coming decades, and the larger the environmental benefits of PEVs, the more that purchase subsidies and other policies contribute to achieving those targets. The efficacy of the PEV subsidies depends on their environmental benefits.2 The environmental benefits of PEVs remain uncertain, however. Compared with gasoline- and diesel-powered vehicles, PEVs reduce emissions from vehicle fuel combustion but increase emissions from electricity generation. Many consumers state that environmental concerns affect decisions to buy PEVs, yet one-quarter of US consumers think PEVs have little or no environmental benefit, and another quarter think those benefits are moderate (Krosnick and MacInnis 2020). Use of fossil fuels for power generation varies temporally and spatially; at most times and locations, electricity generation for PEV charging increases emissions of CO2 and local air pollutants, such as sulfur dioxide (SO2) (Yuksel et al. 2016; Holland et al. 2019). Some research indicates that, given the current reliance on fossil fuel use in the electricity sector, on average PEVs reduce carbon dioxide (CO2) emissions. Research that accounts for the expected shift away from fossil fuels for electricity generation over the coming decades tends to conclude that PEVs will reduce emissions, but under certain assumptions, PEVs may increase emissions (Babaee et al. 2014).