EPA commenced a rulemaking process in 1980 to revise its fuel economy labeling procedures, and analyzed a vast amount of in-use fuel economy data as part of that rulemaking.30 In 1984, EPA published new fuel economy labeling procedures that were applicable to 1985 and later model year vehicles.31 The decision was made to retain the FTP and highway test procedures, primarily because those procedures were also used for other purposes, including emissions certification and CAFE determination. Based on the in-use fuel economy data, however, it was evident that the final fuel economy values put on the labels needed to be adjusted downward in order to reflect more accurately consumers’ average fuel economy experience. The final rule, therefore, included downward adjustment factors for both the city and highway label fuel economy estimates. The city values (based on the raw FTP test data) were adjusted downward by 10 percent and the highway values (likewise based on the raw highway test data) were adjusted downward by 22 percent.32

In the early 2000s, EPA again began investigating the accuracy of the fuel economy label estimates, and concluded that driving behavior (e.g., higher average speed and acceleration) and other factors (such as the use of ethanol as a gasoline blending agent) had changed significantly since the correction factors were implemented in 1985, leading again to a widening gap between real-world fuel economy and the label estimates that consumers saw when shopping for new vehicles. During the development of vehicle emissions regulations in the late 1990s, EPA had already conclusively found that the city and highway tests did not adequately represent real- world driving, and in December of 2006 EPA finalized new test methods for calculating the fuel economy label values.33

The 2006 final rule made three important changes. First, EPA’s new methods brought the miles per gallon estimates closer to consumers' actual fuel economy by including factors such as high speeds, quicker accelerations, air conditioning use, and driving in cold temperatures. These revised fuel economy estimates also reflect other conditions that influence fuel economy, like road grade, wind, tire pressure, load, and the effects of different fuel properties. The new estimates took effect with model year 2008 vehicles. Second, EPA now requires fuel economy labels on certain heavier vehicles up to 10,000 pounds gross vehicle weight, such as larger SUVs and vans. Manufacturers will be required to post fuel economy labels on these vehicles beginning with the 2011 model year. Third, to convey fuel economy information to the public more effectively, EPA updated the design and content of the label. The rule required that new labels be placed on vehicles manufactured after September 1, 2007. The fuel economy for each vehicle model continues to be presented to consumers on the label as city and highway MPG estimates.