The U.S. Environmental Protection Agency (EPA) is proposing new methods for determining fuel economy estimates, which will first be applied to 2008 model year vehicles. As required by the Energy Policy Act of 2005, these methods account for more real-world driving conditions in calculating the city and highway miles per gallon (mpg) estimates that appear on a vehicle’s window sticker.

Last revised in 1985, mpg estimates are currently determined by two tests performed under mild climate conditions, at acceleration rates and driving speeds generally lower than those of most drivers, and without the use of accessories like air conditioning (AC). The three new proposed factors were previously accounted for by across-the-board adjustments rather than vehicle-specific testing and include factors such as high-speed, fast acceleration driving, the use of AC, and operation in colder temperatures. In addition, the EPA has proposed adjustments to better account for road grade, wind, tire pressure, load, and the effects of different fuel properties.

Once the new methods are in place, the EPA expects mpg estimates to drop for city driving by 10–20 percent from the original estimate for cars and trucks and by 5–15 percent for highway driving. Hybrid vehicles will also be affected because the nature of their technology makes their fuel economy more sensitive to factors such as cold weather and AC use. Hybrid city mpg estimates are predicted to drop 20–30 percent while highway mpg estimates may fall about the same percent as that for conventional cars. The EPA cautions that because some automobiles are affected by factors more than others, the impact of the new methods will vary from vehicle to vehicle.

The EPA cites two essential purposes for fuel economy estimates. First, they provide consumers a tool to comparison shop when buying a vehicle. Second, they inform consumers of a reasonable range of fuel economy that they can expect to achieve. When shopping for a vehicle, fuel economy information can be found by looking at a car’s mpg window sticker. This sticker is also undergoing revisions to its format and text in order to more clearly convey information. Four label options are under consideration, and they can be found at www.epa.gov/fueleconomy.

The new fuel economy estimate methods were initially proposed on January 10, 2006. The EPA is providing a sixty-day comment period for the proposal and will hold a public hearing after it is published in the Federal Register.

Image of the current fuel economy label
Images of the proposed fuel economy labels Please visit http://www.epa.gov/fueleconomy/labels.htm for more information or to see additional labels.