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

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

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america continues to lag in making engines more gas efficient. 20 years ago this discussion started but the authorities keep allowing our sad auto companies to not meet higher mpg rates that overseas has.

Folks should note the proposed EPA/DOT window sticker makes a great step in the right direction; it inverts the miles per gallon to the more usable (and easier to compare) gallons per 100 miles.

Using miles per gallons hides the huge difference between gas guzzling cars, and exagerates the small difference between gas sipping cars. That is, a 5 mpg difference between 10 mpg and 15 mpg is much more important than the same between 35 mpg and 40 mpg.

Presenting the consumption comparison as between 10 and 6.7 gallons/100 miles (for the guzzlers) and 2.9 and 2.5 (for the sippers) shows the incremental improvement is huge for the guzzlers and small for the sippers.


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