Few auto industry power players are satisfied with the calculations that award the Chevrolet Volt a stellar 230 miles a gallon (which is topped by the Nissan Leaf battery car at 367). Those numbers are based on a draft Environmental Protection Agency standard for plug-in hybrids and battery cars. But the agency says that work isn’t complete, and it is searching for meaningful ways to present the information to car buyers on the window sticker.
The E.P.A. and the Transportation Department issued their proposed rule-making for combined greenhouse gas and corporate average fuel economy standards on Sept. 15. The agency admitted that designing test procedures and calculations for advanced technology vehicles “can be very complicated” and that what it called “adjustment factors” needed to be weighed. There’s certainly no consensus on which approach will resonate with consumers, and many admit that the advantage of measurements in miles a gallon is sheer familiarity....
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