Crossovers complicate fuel-efficiency distinctions between light trucks and passenger cars, according to a U.S. Energy Information Administration (EIA) brief.

Fuel economy standards of light-duty vehicles are normally determined through vehicle footprints, which are defined by the rectangular area between the contact points of a vehicle’s four wheels and the ground.

While crossovers have the appearance of light trucks such as minivans, pickup trucks, and sport-utility vehicles, they share closer design elements to passenger cars, which have smaller vehicle footprints and use more fuel-efficient engines.

In 2016, crossover sales constituted 32% of the light-duty vehicle market, according to automotive analysis group Wards Automotive. The growing popularity of crossovers and their ambiguous classification has complicated the analyses of fuel efficiency trends and vehicle sales. For example, crossovers that were considered light trucks contributed to the overall weighted average of light truck sales.

Government agencies and organizations also use different metrics to classify light-duty vehicles. The Bureau of Economic Analysis, for example, distinguishes light trucks and passenger cars based on vehicle weight limits and appearance, categorizing crossovers as light trucks.

Government organizations like the National Highway Traffic Safety Administration and the U.S. Environmental Protection Agency based fuel economy standards on specific characteristics, meaning crossovers will be classified as passenger cars or light trucks depending on criteria like rider capacity, open bed, and availability of all-wheel drive.