How the EPA Tests Fuel Economy: The Five Test Cycles

EPA fuel economy ratings come from laboratory tests: a vehicle is driven on a dynamometer, which works like a treadmill for cars, through standardized driving schedules. Results from five kinds of test are used to build the city and highway values on the window sticker. Automakers supply most of the data, and the EPA audits it and re-tests a share of vehicles itself.

Key takeaways

• The dynamometer lets every vehicle follow the same speed trace, so ratings are comparable across models.
• Five tests cover city driving, highway driving, high speed with hard acceleration, hot weather with air conditioning, and cold weather.
• Manufacturers provide the data used for labels. The EPA says it confirms approximately 15% of all test results at its National Vehicle and Fuel Emissions Laboratory (NVFEL) in Ann Arbor, Michigan.
• Since the 2008 model year, the method includes faster speeds, air conditioning and cold weather, which lowered estimates for all vehicles.

Who runs the tests

The EPA defines the test methods and the calculation of label values, but it is the manufacturers that are responsible for providing the fuel economy data used for labeling, testing at their own facilities. The EPA audits that data and runs its own tests on some vehicles. For electric vehicles and plug-in hybrids, EPA documents state that the EPA performs confirmatory testing on all new light-duty models of those types.

Manufacturers test one representative vehicle for each combination of loaded vehicle weight class, transmission class and basic engine, rather than every trim or option package. That is one reason two trims of the same model can share a rating.

The five test cycles

The EPA’s testing page lists five cycles, and fueleconomy.gov publishes the schedules behind them:

Test	What it represents	Average speed	Top speed	Distance
City	Stop-and-go urban driving, engine started cold	21.2 mph	56 mph	11 miles
Highway	Rural and Interstate driving, engine warm	48.3 mph	60 mph	10.3 miles
High speed (US06)	City and highway driving at higher speeds with harder acceleration and braking	48.4 mph	80 mph	8 miles
Air conditioning (SC03)	Hot conditions, with the air conditioner set to cool	21.2 mph	54.8 mph	3.6 miles
Cold (city test at 20 degrees F)	Cold-start driving in cold weather, with heat and defrost settings	21.2 mph	56 mph	11 miles

The SC03 test accounts for air conditioning under hot outside conditions, with a 95 degrees F sun load. The cold test is the city schedule run in a laboratory at 20 degrees F. The city, highway and high-speed tests run without heating, ventilation or air conditioning in operation.

From five tests to one label number

For many vehicles the full set of tests is run and combined. The EPA’s procedures also allow a derived approach, in which city and highway test results are adjusted with factors based on data from vehicles that were fully tested, so not every model needs every cycle in the lab. The label’s city and highway values are then combined into the headline number using a 55% city and 45% highway weighting; see city vs highway MPG and the combined rating.

How electric vehicles and plug-in hybrids are tested

Electric vehicles are driven in repeated laboratory cycles until the battery is depleted, then recharged to measure the energy used. The recharge energy includes charger losses. Range and energy use are then adjusted for real-world factors. EPA documents say the label can use a factor of 0.7 applied to the test results, and that most EVs use that approach or an equivalent. Label range combines city and highway at the same 55% and 45% weights.

Plug-in hybrids are tested in two operating conditions: charge-depleting, starting with a full battery, and charge-sustaining, starting with an empty one. How plug-in hybrids are rated explains how the two results are combined.

Why the method changed over time

The EPA updated its method in 2008 to account for faster speeds and acceleration, air conditioner use and colder outside temperatures, and fueleconomy.gov notes that these changes lowered fuel economy estimates for all vehicles. For model year 2017, the EPA updated some of the calculations used to estimate fuel economy based on actual vehicle data from the 2011 to 2016 model years. Most vehicles were not affected, some estimates fell by 1 mpg, and a small number were 2 mpg lower. See why model year ratings change.

What the tests are and are not

Laboratory testing is designed for repeatable comparison. It is not a prediction of your own mileage, a point covered in real-world MPG vs the EPA label. To see how Gallonly turns label values into dollars, read the methodology.