WARREN, Mich.--General Motors' announcement on Tuesday that it expects that the Chevy Volt will get an eye-popping 230 miles per gallon begs an obvious question: how can the mileage of electric vehicles be compared to gasoline cars?
It's a problem that the Environmental Protection Agency is working on with the Department of Energy, the Society of Auto Engineers, and California, an EPA representative said on Wednesday. But that system for testing mileage is still in development and not yet public.
The EPA also put out a statement on Tuesday saying that it has not tested the Volt for mileage yet and "cannot confirm the economy values claimed by GM." GM said that its mileage estimate, including triple digit combined city and highway driving, was based on a draft methodology developed by the EPA.
The lack of verifiable tests, however, hasn't stopped automakers from tantalizing consumers. The all-electric Nissan Leaf, due in late 2010, boasts the equivalent of 367 miles per gallon, and the electric Tesla Roadster claimed over 100 miles per gallon mileage as well.
Pressed on how mileage numbers for the Volt were arrived at, GM executives offered some details, saying that the number will vary depending on how far people drive before they replenish the car's batteries.
The draft EPA methodology figures that a plug-in electric vehicle driver will go a certain number of miles on batteries alone and then another portion on the gasoline engine, explained Frank Weber, the global vehicle line executive for the Chevy Volt. To arrive at the mix between battery versus gasoline, the EPA is studying average American driving patterns, executives said.
The EPA is also developing another, less familiar metric for electric vehicles. In the Volt's case, it will take 25 kilowatt-hours to go 100 miles. Weber said the models behind the EPA methodology are "robust," adding that he expects the EPA to disclose more about the tests later this year.
To come up with 230 miles per gallon for city driving, GM assumes that Volt owners charge the car's batteries once a day, which enables them to do the majority of their driving from electricity drawn from the socket. The Volt, due late next year, is designed to run 40 miles on electric charge and then use a gasoline engine to sustain the battery for longer trips.
Misleading? Triple digit combined fuel efficiency is certainly impressive--the Toyota Prius and Honda Insight hybrids both sport combined mileage of about 50 miles per gallon depending on driving style.
But immediately after GM's announcement, people began complaining that the claim is misleading.
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