Recently, the U.S. Environmental Protection Agency (EPA), in collaboration with the California Air Resources Board, adopted new corporate average fuel economy (CAFE) standards, which mandate that by 2016, the fleet of cars and light trucks that automakers sell in the U.S. must average 35.5 miles per gallon. Congress first enacted CAFE standards in 1975 to improve the fuel economy of U.S. passenger cars, largely as a response to fuel shortages caused by the 1973 Arab oil embargo.
The increased miles-per-gallon rating sounds great. But the real-world average fuel economy that cars and light trucks get in 2016 won’t be nearly that good, and the EPA knows it. It’ll be at least 30 percent lower, about 25 mpg.
How can this be? Simply put, the EPA uses different test procedures to calculate CAFE standards from the ones it uses to determine the fuel-economy numbers posted on the window stickers of new cars.
A bit of background: The EPA determines a car’s fuel-economy rating by performing tests on a dynamometer (a treadmill-like device for cars). In 1972, the EPA began using two tests, one for city mpg and another for highway mpg. Then in the 1980s, the EPA decided the tests didn’t accurately predict real-world mpg, so they adjusted the ratings downward by 10 percent for city driving and 22 percent for highway driving. At the time, the adjusted numbers were reasonably accurate, and they were posted on new-car window stickers through model year 2007.
However, since the 1980s, cars and the way we drive them have changed. Speed limits have increased, and freeways are more congested. People typically drive faster, and they accelerate more rapidly. In addition, vehicles made in the last 20 years are larger and more powerful. By the late 1990s, drivers noticed that their cars got much lower fuel economy than the EPA estimates.
Beginning with model year 2008—based in large part on scientific input from the Auto Club’s Automotive Research Center—the EPA combined the results of three new dynamometer tests (which included driving at higher speeds, aggressive driving, driving on hot days with the air-conditioning on, and starting up on cold days) with the existing tests. The result was a more-accurate method of estimating mpg for 2008 and later model years—and the new ratings were at least 30 percent lower than the unadjusted test results.
Here’s the rub. CAFE standards have always been based on the testing methodology from the 1970s, even though it’s acknowledged to be inaccurate, and proposed regulations will continue this practice.
So in effect, there’s a double standard—inaccurate methods of measuring mpg for CAFE purposes and a relatively accurate method used to calculate the numbers on new-car window stickers. (The EPA and the National Highway Traffic Safety Administration [NHTSA], the two federal agencies charged with developing and implementing mpg standards, can’t even agree on the existing standard for 2016. EPA allows for credits for air-conditioning improvements and calls it 35.5 mpg, but NHTSA calls it 34.1 mpg.)
Again, how can this be? A simple, one-word answer: politics. In 1975, Congress passed the Energy Policy and Conservation Act (EPCA), which established CAFE standards and mandated the specific test procedures to be used for CAFE compliance—the two dynamometer tests referred to earlier.
To change the way CAFE is calculated, Congress would have to amend the original EPCA language and specify changes in the testing procedures. Such a move would likely upset carmakers, because their products would look much less “environmentally friendly.” Unfortunately, modifying the EPCA’s language isn’t high on Congress’s to-do list.
The Auto Club thinks it’s time to start talking honestly about CAFE regulations and proposals and to calculate CAFE mileage ratings using EPA’s most recent and most accurate methodology. As CAFE requirements increase, so does the discrepancy between real-world fuel economy and the EPA’s fictional numbers. An accurate method of measuring miles per gallon exists—let’s use it.
Steve Mazor is the manager of the Auto Club’s Automotive Research Center.
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