AAA—the American Automobile Association—has labelled as outdated the methodology the EPA uses to establish its mileage ratings. The association is now lending its support to new legislation in Congress (the “Fuel Efficiency Truth-in-Advertising Act of 2005”) that would require EPA to update its fuel economy testing procedures.

Each year, AAA car review experts test hundreds of vehicles under “real world” driving conditions and come to the same conclusion as many motorists—the actual miles per gallon achieved during the daily use of a vehicle generally falls well short of Environmental Protection Agency (EPA) estimates.

AAA test drives are neither standardized nor scientific, but the nation’s organization for motorists nevertheless says that its test results may be more meaningful to consumers as they make car-buying decisions.  AAA’s testers put vehicles through a range of driving cycles that include stop-and-go traffic, climbing steep grades, trips to the grocery and a combination of both highway and city driving.

Their full vehicle reviews, and samples of the mileage findings, are on the AAA website.

I took the AAA sample findings and compared them to the combined (city/highway) EPA mileage rankings of the same vehicles. On average, the AAA mileage was 17% worse than the EPA’s. The mean variance was 15.5%, the largest variance was 39.5% and the smallest 7.4%.

Objective testing of anything is tricky business, requiring standard procedures and measurements.  Subjective testing is skewed by the vagaries of the tester or the process. However, results that are, in every case, lower than the EPA’s figures do point to a need for some revised methodology—or for some better driver training.

A driver’s behavior has a great deal to do with actual fuel efficiency—the problem is, there hasn’t been a mechanism for getting realtime feedback on driver performance. At best, it’s the dismay when you need to tank up again sooner than expected; at worst, a traffic ticket.

Green Car Congress contributor Mikhail Capone writes that one solution might be to make the realtime consumption displays found in hybrids standard in all cars. 

I believe that MPG-meters in all cars would make a huge different overall in fuel-efficiency, just like the speedometer allows you to know how fast you are really going and adjust your driving accordingly. With a MPG gauge in all cars, people would know that they are getting crappy mileage, and they’d see the effect of racing from stop signs to the next red-light. A minority of people would not change their driving habits, but most people want to spend less on gas, not more.

Good idea.