Consumers Need More Reliable Automobile Fuel Economy Data

Since 1976, purchasers of new automobiles in the United States have relied on fuel economy test data to help choose fuel-efficient vehicles. Under a fuel economy labeling program administered by the Environmental Protection Agency (EPA), in cooperation with the Departments of Transportation and Energy and the Federal Trade Commission, every automobile manufactured for sale and use in the United States is required to display a label showing its tested fuel economy, its estimated annual fuel costs, and the fuel economy range of comparable vehicles. Since the program began, there have been complaints of discrepancies between the EPA fuel economy test results and consumers' reported on-road fuel economy. GAO was asked to determine why these discrepancies exist, whether better measures of fuel economy can be developed, and whether better ways of disseminating this information to consumers can be devised.

Differences between the EPA figures and drivers' on-road mileage figures result from many factors including variances in travel environments, driver habits, vehicle conditions, and design changes. In addition to these factors, discrepancies which are caused either by the test procedures themselves or by automobile advertising have caused consumers to become increasingly skeptical of the program. EPA proposes to revise the fuel economy labeling program by, among other things, adjusting the test values to better represent the gas mileage consumers are obtaining on the road. Its proposal includes a plan to apply an adjustment factor to each automobile label value which would account for the average discrepancy between the fuel economy test results and consumers' on-road data. Although manufacturers generally support this plan, some are concerned over how the factor should be calculated. Recent studies comparing the fuel economy test results with on-road experience indicate that separate adjustment factors may be required to reflect new automobile technologies. However, more research data are needed before any definite conclusions can be drawn on how changing technologies could affect the adjustment factors. Further, if proposed EPA revisions to the fuel economy labeling program become effective, education programs will be needed to adequately inform consumers of the program adjustments and limitations.