AAA: Drivers, Not Cars, Are Responsible for Fuel-Economy Discrepancies

A new AAA study finds that a lot of drivers still don’t think EPA car-window stickers report accurate real-world mileage. In reality, real-world variations are largely due to driving conditions and behavior, not individual automakers or the EPA. The study’s results come after a tumultuous period for EPA mileage, with automakers from Hyundai-Kia to Ford downgrading mileage, in some cases with big financial penalties.

Related: Loopholes and Fuzzy Math: The Tangled Science of MPG Ratings

Released today, the study analyzed some 37,000 driver-reported mileage records on the EPA’s website. AAA also lab-tested several cars and surveyed about 1,000 adults. Here’s what it found:

• About a third of consumers don’t believe EPA window stickers reflect accurate real-world fuel economy. That’s something they weren’t originally intended to do, we might add.
• Still, 81.8 percent of driver-reported mileage actually exceeds EPA numbers for drivers’ respective cars. Overall driver-reported mileage is 12 percent higher than the combined EPA figures, though AAA admitted that such self-reported numbers are of “limited statistical use” because the estimates can’t be verified.
• Drivers of cars with manual transmissions or diesel engines (or both) reported the highest gains versus the EPA mileage for their cars. Truck drivers with turbo V-6 engines and sedan drivers with turbo four-cylinder engines, meanwhile, reported significantly lower mileage than their cars’ EPA ratings.
• AAA and the Automotive Club of Southern California’s Automotive Research Center identified three cars with particularly low owner-reported mileage relative to their EPA numbers and tested them through various EPA cycles on laboratory dynamometers. They also put each car through a month of real-world driving. All three cars achieved (or beat) EPA numbers, and AAA concluded that your mileage varies more based on how you drive, where you drive and the condition of your car — not any sort of discrepancy between the car and its EPA figures.

How much do different driving styles affect your mileage? AAA says it plans to release more test results in late 2015, and it will break down the gas-sucking effects of activities like hard acceleration and excessive idling. Stay tuned.