E.P.A. Says M.P.G. for Electric Cars and Plug-in Hybrids Is a Work in Progress

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.

In a letter released on Wednesday (but written Sept. 23), the agency said it would “initiate a new rule-making to explore in detail the information displayed on the current fuel economy label and the methodology for deriving that information.” The E.P.A. letter also said it was seeking input on consumer labels that could “provide practical, usable and meaningful information to vehicle purchasers” interested in battery electrics, plug-in hybrids and “other advanced technology vehicles.”

The E.P.A.’s letter was in response to a Sept. 10 proposal from Israel’s ETV Motors, which is working on battery technology as well as a hybrid concept that uses a micro-turbine to replenish an E.V.’s batteries. In an interview, ETV’s chief operating officer, Arnold Roth, said the company wrote to the United States agency because “the world needs the E.P.A. to take the lead. What the E.P.A. does will have a ripple effect into all markets.” The United States, said Dror Ben-David, ETV’s chief executive, “is a leader in rule-making.”