The fuel efficiency of a personal highway vehicle (cars, light trucks, motorcycles) measures the distance traveled per unit of energy consumed by the vehicle. In the United States fuel efficiency is measured in miles per gallon (mpg), while in the European Union, it is measured in liters of gasoline equivalent per 100 km (Lge/100 km). This article focuses on gasoline-powered, personal passenger cars and trucks in the United States, including plug-in hybrid electric vehicles (PHEVs). In the United States, personal vehicles account for about 57% of all energy used in transportation (air, land, water) and about 15% of total national energy use.1
Vehicle weight is an important determinant of fuel efficiency due to basic physics.2 A heavier vehicle has greater inertia and therefore requires more energy to get it moving. A heavier vehicle has greater rolling resistance (friction), which describes the energy that must be sent to the tires to keep the vehicle moving at a constant speed.
Model year 2023 vehicles evaluated by the U.S. Environmental Protection Agency (EPA) demonstrate the relationship between weight and fuel efficiency. The EPA tested gasoline-powered passenger cars and trucks that ranged in weight from about 2400 to 7000 pounds, and in fuel economy from 12 to 65 mpg. Not surprisingly, cars tend to be lighter and more fuel-efficient than pickup trucks and SUVs.
But note that there are significant variations from the general weight/efficiency connection. For example, the Porsche 911 GT3 Touring and the Toyota Camry LE/SE each weigh about 3600 pounds. But the Porsche gets 22 mpg while the Toyota gets 47 mpg. The principal reason for the difference is that the Porsche has a much larger engine – a whopping 502 horsepower – compared to the Toyota, which comes in at 203 horsepower.
Vehicle weight takes on added importance in light of changes in the vehicle preferences of American drivers. Since the mid-1970s American consumers have shifted dramatically away from conventional sedans and wagons, first to minivans and pickup trucks, and more recently to car and truck SUVs.3 This represents a general shift from lighter to heavier vehicles.
But vehicles have gotten heavier even within each class of vehicles. Most vehicle types got lighter in the immediate aftermath of fuel efficiency standards set for vehicle manufacturers by the EPA in 1975. But always attuned to the preferences of American drivers, manufacturers, found clever ways to meet the efficiency of standards while simultaneously increasing the size and weight of vehicles. The average car in 2023 weighs 18% more than it did in the mid-1980s. The average pickup truck gained 43% more weight in the same period.
It is a testament to the ingenuity of automotive engineers that they improved fuel economy as vehicle size increased. But make no mistake about it: a heavier vehicle requires more energy to operate than a lighter vehicle. When powered by liquid fuels, such as gasoline and diesel fuel, a heavier vehicle uses more fuel and thus has greater lifecycle health and environmental impacts across the energy supply chain.
1 Davis, Stacy C., and Robert G. Boundy. Transportation Energy Data Book: Edition 40. Oak Ridge National Laboratory, 2022, https://doi.org/10.2172/1878695.
2 Natural Resources Canada, Learn the facts: Weight affects fuel consumption, Link
3 U.S.Environmental Protection Agency, “Automotive Trends Report 2022,” Accessed June 16, 2023, https://www.epa.gov/automotive-trends