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EPA fuel economy labeling: Is there a better metric than MPG or MPGe?

October 27, 2010 |  3:48 pm

EPAfueleconomylettergradeThe U.S. Department of Transportation and Environmental Protection Agency face twin and equally daunting tasks as they revise the fuel economy labels as mandated by the 2007 Energy and Independence Security Act.

Not only must they incorporate accurate fuel economy, greenhouse-gas emissions and smog-forming emissions ratings for gas-powered passenger vehicles, but also for plug-in battery-electrics that derive power from other sources.

As more cars come on the market powered by electricity, E85, hydrogen and other fuels, miles per gallon -- as a metric -- is problematic. But is the public ready for an entirely new metric?

Last week, at a public hearing in Los Angeles, Robert Bienenfeld of American Honda Motor Co. suggested a new direction. Instead of miles per gallon, he proposed miles per purchased unit of energy.

"In the case of electricity, it would be miles per kilowatt hour. With ethanol, it would be miles per gallon of E85. With diesel, it would be MPG of diesel fuel. It would be intellectually inconsistent to turn all metrics into MPG equivalents [or MPGe] when no one will purchase electric, diesel or E85 in MPGe units," Bienenfeld said. MPGe converts alternate fuels into a miles per gallon of gasoline equivalent.

Bienenfeld recognized that consumers do not like new metrics, but over time, he said, drivers of vehicles that consume electricity will want to know their miles per kilowatt hour, not their MPGe.

He suggested two ways for consumers to compare any two technologies: an annual fuel cost metric and  one for well-to-wheel carbon dioxide emissions that factor in the upstream emissions of creating a vehicle’s fuel as well as the emissions caused in driving the vehicle.

Focusing only on what comes out of a tailpipe to calculate greenhouse-gas and smog-forming emissions excludes upstream emissions, i.e., the source of electricity used to power plug-in electric vehicles.

"New metrics are scary," Bienenfeld said, "but if a customer is going to buy an electric vehicle or a plug-in hybrid, it’s important they learn what they’re getting. We shouldn’t be afraid. Otherwise we have no business even showing the public new technologies."

-- Susan Carpenter

Graphic: U.S. Environmental Protection Agency