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Study Challenges Assumptions About Electric Vehicle Usage

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Nov 7 2023Reviewed by Laura Thomson

The widespread adoption of electric vehicles (EVs) plays a critical role in the United States' efforts to reduce carbon emissions in its energy system. As the number of EV owners in the US continues to rise, gaining insight into their driving habits becomes crucial for various aspects, including climate and energy models, as well as policy and energy planning in the country.

Up to this point, modelers and regulatory agencies like the Environmental Protection Agency (EPA) have operated under the assumption that EV owners drive their vehicles roughly the same number of miles as owners of gasoline-powered cars. However, recent research published in Joule challenges this assumption, suggesting we might have overestimated emissions reductions achieved through EV adoption.

In one of the most extensive studies on EV mileage to date, researchers from George Washington University and the National Renewable Energy Laboratory analyzed odometer data from 12.9 million used cars and 11.9 million used SUVs spanning the years 2016 to 2022. Their findings indicated that battery electric vehicle (BEV) cars covered nearly 4,500 fewer miles yearly than gasoline cars.

This gap in mileage held for both cars and SUVs: electric cars averaged 7,165 miles annually. In comparison, gas-powered cars covered 11,642 miles annually, and electric SUVs traveled 10,587 miles annually, while gasoline-powered counterparts covered 12,945 miles annually.

People often assume that buying an EV is good for the environment, and it generally is, but the impacts scale with mileage. Our study shows that the current generation of EV owners aren’t using them as much as gas cars. For maximum impact, we need the highest-mileage drivers behind the wheel of EVs rather than low-mileage drivers.

John Helveston, Study Co-Author and Assistant Professor, Engineering Management and Systems Engineering, George Washington University

Due to the typically lower emissions associated with EVs throughout their lifetime, substituting a higher-mileage gasoline vehicle with an EV leads to greater emissions reductions, assuming all other factors remain the same.

The researchers also compared the mileage of Tesla electric vehicles (BEVs) and non-Tesla BEVs, considering Tesla's prominence in the EV market, higher-range vehicles, and a well-established fast-charging network. Nonetheless, they discovered that although Teslas were driven more than other EVs, they still logged fewer miles on average than traditional gasoline cars. The study did reveal that plug-in hybrid and hybrid vehicles were driven at a similar rate to gasoline vehicles, however.

This study carries significant implications for policymakers and regulators responsible for formulating and enacting emissions regulations. The findings challenge existing assumptions regarding the mileage of electric vehicles, potentially impacting the accuracy of emissions models and regulations. To illustrate, the most recent analysis by the EPA presumes that EVs are already being driven the same miles as traditional gasoline cars, which this study calls into question.

If you’re going to craft a model that predicts how much emissions can be saved from EV adoption, that model heavily depends on how much you think EVs will be driven. If federal agencies are overestimating true mileage, that results in overestimating the emissions savings. We need to better understand not just who is buying EVs, but how they’re driving them. What trips are EV owners substituting for a cleaner trip in an EV, and what trips are EV owners not taking?

John Helveston, Study Co-Author and Assistant Professor, Engineering Management and Systems Engineering, George Washington University

Although not the primary focus of the study, Helveston mentioned a couple of factors that could be influencing the driving patterns of EV owners. These factors include a potential lack of charging infrastructure, which may restrict EV owners' capacity to embark on longer-distance journeys reliably.

Researchers propose that households with multiple vehicles may also contribute to the findings; individuals who own EVs often possess multiple vehicles and may distribute their annual mileage among them, reducing the overall mileage on their EVs.

“The magnitude of data used in this study posed several technical challenges, but I hope our efforts can inform policy around the impacts of EV adoption”, adds Lujin Zhao, a GW PhD student who led the study.

The study's findings also carry implications for the electricity grid, as they suggest that the expected electricity demand from EV adoption may be less than what utilities have been preparing for.

The researchers emphasize the importance of recognizing that manufacturing a battery-powered EV usually entails higher initial emissions than producing a gasoline vehicle. Helveston and the research team underscore that it will take a longer time to offset these higher upfront emissions if people are not driving their EVs enough.