To determine vehicle fuel economy ratings and what factors impact fuel economy, vehicles are tested under controlled conditions using a standardized procedure. Original equipment manufacturers (OEMs) are required by federal law to test at least one representative vehicle for each light-duty model and must report the results to the U.S. Environmental Protection Agency (EPA), which reviews the results and confirms about 10 to 15 percent of the vehicles through tests at the National Vehicles and Fuel Emissions Laboratory (NVFEL).

In a laboratory, the vehicle is placed on a machine called a dynamometer that simulates the driving environment and can be adjusted to account for wind resistance and the vehicle’s weight. A professional driver runs the vehicle through a prescribed driving routine at various speeds to simulate typical trips in the city or on the highway.

To measure the fuel economy of the vehicle, a hose is connected to the tailpipe to collect the engine exhaust. The carbon in the exhaust is then measured to calculate the amount of fuel burned during the test. This process is more accurate than using a fuel gauge.

Some vehicle types are exempt from fuel economy testing requirements, including pickup trucks and cargo vans with gross vehicle weight ratings (GVWR) greater than 8,500 pounds; passenger vehicles, including SUVs and passenger vans, with GVWR of 10,000 or more; and motorcycles.

To improve fuel economy, vehicle owners can drive less aggressively, observe the speed limit, reduce cargo and avoid excess idling. Maintenance practices that include keeping tires fully inflated, keeping the engine properly tuned and using the recommended grade of motor oil can also improve vehicle fuel economy.

For more detailed information about the factors that affect vehicle fuel economy, refer to the Factors that Affect Fuel Economy website at FuelEconomy.gov.

Contributed by the Clean Cities Technical Response Service Team. For more information, call 800-254-6735 or email [email protected].