No Wonder your “Actual Mileage May Vary”

Millions of budget-conscious Americans consider the m.p.g. ratings on window sales stickers or listed on consumer websites before buying or even renting a car.
What they might not know is that very few of those fuel-economy claims — only about 15% — are verified by regulators. Even then, actual results vary from vehicle to vehicle, model to model and driver to driver.
In addition, the meaning and definition of m.p.g. has changed as hybrid vehicles that combine electricity and gas-powered technologies have turned the rating into more of a theoretical index rather than a mathematical calculation of the actual amount of gas used.
The automakers do their own testing, filling out forms and assigning their own m.p.g. ratings. Then the U.S. Environmental Protection Agency reviews the paperwork, but spot checks 150-300 of 1,500-2,000 car models in its National Vehicle and Fuel Emissions Laboratory in Ann Arbor, Michigan. It’s the EPA’s only fuel economy laboratory, and the testing area is under heavy lock and key.
Up to a 3% difference between the company’s rating and the EPA’s test results is allowed — more than that and penalties kick in. If that happens, it’s the EPA’s figure that goes on the window stickers. If it’s more than 3%, the carmaker may ask the EPA to retest the vehicle or else the EPA number is used.
“It is rare to see a difference because the procedures are literally hundreds of pages of detailed directions. Automakers have a clear compliance roadmap, and we know EPA is checking randomly,” Gloria Bergquist, spokeswoman for the Alliance of Automobile Manufacturers, said in an e-mail. She called the penalties for falsifying reports a “substantial deterrent:” up to $37,500 per vehicle, per day, plus jail time for the person who falsified the report.
The m.p.g. rating has never been an exact science and has always been considered the “expected range” a driver can expect.
The actual performance differs for each person depending on driving style, (Do you hit the brakes hard? Do you peel out from stoplights?), weather conditions, road surfaces and the mix of city and highway driving.
In Ann Arbor, the EPA tests vehicles on a chassis dynamometer that is a very sophisticated treadmill atop a drum approximately 5 feet in diameter. It’s connected to an electric motor or generator that provides resistance. In the small test cell that echoes with noise, the car is strapped in, wedges are placed beneath the wheels and hoses attached to the exhaust pipe to capture what comes out.
“Tailpipe emissions go into a hose. That emission goes through exhaust analyzers. The hydrocarbons, the carbon monoxide, the nitrous oxide, they’re able to analyze all those,” said a high-ranking laboratory overseer.
The test comprises five cycles of between 10 and 30 minutes long — city driving, highway driving, high-speed aggressive, city driving in 20 degrees and 95 degrees with the air-conditioning on and heat-radiant lamps beating down on it.
The driver inside tries to trace the route displayed on the flat-screen monitor.
Whenever gas prices spike, fuel efficiency and federal regulation of the standards — called CAFE or Corporate Average Fuel Economy — are pushed into the spotlight. Also, the m.p.g. rating process has changed with the mainstreaming of hybrid technologies that have pushed up ratings as more of a comparative index related to cost savings because electricity is not sold in gallons.
That changing meaning of m.p.g. was highlighted this year when a Honda Civic hybrid owner in California won her small-claims court case against the car manufacturer, saying the vehicle didn’t deliver the 50 m.p.g. the company claimed.
The plaintiff, herself a lawyer, chose to pursue the case on her own, rather than join a class-action settlement that paid a couple hundred dollars plus a rebate on a new Honda. She won a nearly $10,000 judgment on her own, but the decision was overturned in May.
The second California judge said that m.p.g. ratings are only a guideline and not a promise. He also noted that most people get close to the EPA-tested rate anyway.

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