How the EPA tests fuel economy

New 2008 EPA fuel economy label
New 2008 EPA fuel economy label. Image © US Environmental Protection Agency

The Environmental Protection Agency (EPA) has mandatory fuel-economy tests that must be carried out on all cars (but not all light trucks) sold in the US. Most of the tests are actually carried out by the automotive manufacturers; the EPA tests 10 to 15% of the cars to verify the results.

Old method (2007 and earlier)

The fuel economy tests are run on a dynamometer, a pair of rollers that works like a treadmill for cars.

The rollers can create resistance to simulate factors such as wind drag. The test consists of a city cycle and a highway cycle. All tests are climate-controlled to simulate a 75-degree day and no accessories (such as air conditioning) are used. Two tests, the city cycle test, and highway cycle tests, are carried out as follows:

City cycle

  • Trip length: 11 miles
  • Test time: 31 minutes
  • Number of stops: 23
  • Time spent idling: approx. 18%
  • Maximum speed: 56 MPH
  • Average speed: 20 MPH
  • Engine temp at startup: Cold (75 degrees outside air temperature)

Highway cycle

  • Trip length: 10 miles
  • Test time: 12.5 minutes
  • Number of stops: None
  • Time spent idling: None
  • Maximum speed: 60 MPH
  • Average speed: 48 MPH
  • Engine temp at startup: Warm

New method (2008 and later)

Because the EPA fuel economy estimates did not reflect real world mileage, EPA revised its testing methods in 2007. Among the changes:

  • Higher speeds - up to 80 MPH on the highway cycle
  • Colder temperatures - tests start at 20 degrees Fahrenheit rather than 75
  • More rapid acceleration
  • Use of accessories - the air conditioner will be operated 13% of the time

Results of the new method

The new testing methods dropped city fuel economy estimates by 10% to 20%, with hybrids taking the highest percentage.

Highway estimates will dropped around 5% to 15%.

Current regulations only include vehicles with a GVWR (Gross Vehicle Weight Rating - the maximum permissible weight of the vehicle, fuel, and payload, including passengers) of up to 11,000 lbs, which excludes some trucks.

See fuel economy ratings or find and compare cars at the EPA's fuel economy site, www.fueleconomy.gov.