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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 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)

It's common knowledge that EPA fuel economy estimates do not reflect real world mileage, and are particularly advantageous for hybrids. Because of these known discrepancies, the EPA decided to revise its testing methods. Tests will continue to use a dynamometer. Changes will include:
  • Higher speeds - up to 80 MPH on the highway cycle
  • Colder temperatures - tests will now 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 will drop city fuel economy estimates by 10% to 20%, with hybrids taking the highest percentage. Highway estimates will drop by around 5% to 15%.

The new methods -- which will be accompanied by a new fuel-economy label on the car's price sticker -- will apply to 2008 model year cars manufactured after September 1, 2007. Through June, automakers will be allowed to attach an additional label showing what fuel economy estimates would be using the old test methods.

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 8,500 lbs, which excludes many large SUVs, vans and pickups. By 2011, manufacturers will be required to apply EPA fuel-economy ratings to medium-duty vehicles with GVWRs of 8,500 to 11,000 lbs.

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