UT Study Investigates Gap Between Motorists’ Fuel Economy Estimates and Government Ratings

David GreeneA new study released today from UT’s Howard H. Baker Jr. Center for Public Policy indicates that the gap between government fuel economy estimates and what consumers are reporting has increased for recent model year vehicles.

“There has always been a known gap between the test ratings and what people get in the real world, which historically has been about a 15 percent difference,” said David Greene, one of the authors of the study and senior fellow in the Energy and Environmental Policy program at UT’s Baker Center. “But one of the key findings in our study is that we found this difference has recently increased to about 20 percent. An increase of this size was anticipated by the Environmental Protection Agency and Department of Transportation when they set the new fuel economy standards. The real issue is to be sure the gap doesn’t continue to grow.”

The fuel economy tests are used for two purposes: to determine if manufacturers are in compliance with federal fuel economy and greenhouse gas emission standards, and to inform the public about the fuel economy of the vehicles they buy.

With respect to consumer information, Greene says there have always been differences between what people get on average and what number is reflected on the label of a new car.

But the study found tremendous variability from driver to driver. Because of that, the label value is not a good predictor of what individuals will actually get, which makes the information less useful to consumers.

Researchers analyzed approximately 75,000 individual fuel economy estimates from the Department of Energy’s website fueleconomy.gov. Visitors to the website have been submitting their own fuel economy estimates since 2005. The records cover all model years from 1984 to 2015 and all states in the United States.

“This is a unique resource for understanding how fuel economy estimates used to enforce corporate average fuel economy and greenhouse gas emissions standards relate to real-world outcomes,” said Greene.

Greene said technology exists to give drivers more accurate data that correlates with their driving habits and travel routines.

“For years, people have assumed that the problem with the government’s fuel economy estimates was that they were too high, on average,” said Greene. “But according to the data, the EPA miles-per-gallon numbers do a pretty good job of predicting what the average driver will get. The problem is that very few of us are average. For a car rated 25 miles per gallon, we can be 95 percent sure that the on-road fuel economy any individual driver actually gets will be somewhere between 15 and 35. Consumers need better information than that, and modern information technology may make that possible.”

The findings show that the shortfall between test cycle fuel economy estimates and in-use fuel economy estimates has been increasing since 2005.

According to Greene, the gap should be closely monitored and, if it continues to grow, test procedures or regulations should be adapted to better reflect real-world conditions.

“Manufacturers will spend billions of dollars each year to meet federal fuel economy and emissions standards,” said Greene. “The standards are designed to save consumers several times that in reduced fuel costs. Making sure the standards are working as intended requires knowing what drivers really get on the road. Now it’s more important than ever that we watch this closely to make sure the gap doesn’t get any bigger.”

To view the full report, visit bakercenter.utk.edu/2015/10/01/baker-fellow-greene-investigates-gap-between-motorists-fuel-economy-estimates-and-government-ratings.

For more information about the Baker Center, visit bakercenter.utk.edu.

CONTACT:

Tyra Haag (865-974-5460, tyra.haag@tennessee.edu)