Nancy Johnson (R-CT) and 24 bipartisan co-sponsors have introduced a bill in Congress that calls for the Environmental Protection Agency to improve the accuracy of its protocol for estimation of vehicle fuel economy (i.e., as measured in miles-per-gallon, mpg). According to a press release issued by Representative Johnson’s office,

““America’s car buyers deserve truth-in-advertising when they buy a new car,” said Johnson, who introduced the bill with Rep. Rush Holt (D-NJ) and over two dozen bipartisan co-sponsors. “The current EPA tests clearly mislead car buyers. Car buyers think they’re getting better mileage on the road and a better deal at the pump than they really are. This common-sense bill requires the EPA to update its 30-year-old tests to reflect today’s driving conditions.” The tests used by the EPA to measure fuel economy – the city/highway gas mileage figures that appear on a new car’s sticker – are 30-years-old and are based on car technology from the late 1970s and 1980s. According to government and auto industry experts, the tests produce gas mileage rates that are inflated from anywhere between 10% and 30%. The inflated rates mislead consumers into thinking they are getting better mileage on the road, and a better deal at the gas pump, than they really are.”

Data should be accurate, who is going to argue with that?


If the bill becomes law it may lead to profound effects on actual fuel economy and a political battle waged through EPA estimates of fuel economy. The reason for this is that the government has in place policies governing what is called “corporate average fuel economy” or CAFE standards. Here is how the CAFE program describes it: “Corporate Average Fuel Economy (CAFE) is the sales weighted average fuel economy, expressed in miles per gallon (mpg), of a manufacturer’s fleet of passenger cars or light trucks with a gross vehicle weight rating (GVWR) of 8,500 lbs. or less, manufactured for sale in the United States, for any given model year.” For passenger cars the current standards are 27.5 mpg and for light trucks 21,0 mpg (for details go here.).

And here is the part of the CAFE program that is most important with respect to Rep. Johnson’s proposed bill, “Fuel economy is defined as the average mileage traveled by an automobile per gallon of gasoline (or equivalent amount of other fuel) consumed as measured in accordance with the testing and evaluation protocol set forth by the Environmental Protection Agency (EPA).” The Department of Transportation (DOT) does claim to verify the EPA estimates. Even though Rep. Johnson says that her bill does not “alter or change Corporate Average Fuel Economy requirements,” it could have very significant implications for the auto industry under CAFE.

If it turns out that EPA’s estimates of fuel economy are off by, say, 30% industry-wide, and this is reflected as well in the DOT CAFE program verification of those estimates, then this means that present guidelines of 27.5 mpg and 21.0 mpg are really only leading to fuel efficiency levels of 19.25 mpg and 14.7 mpg! Any changes resulting from Representative Johnson’s bill of the EPA/DOT protocols for estimating fuel efficiency that lead to a downward revision in fuel efficiency estimates will necessarily have the effect of compelling automakers to increase the fuel efficiency of their fleets under CAFE.

If Rep. Johnson’s bill becomes law we will undoubtedly see a vigorous battle over the EPA protocol used to estimate fuel efficiency and a corresponding mapping of political debate over fuel efficiencies onto the technical methods used to calculate them.