Electric Cars' MPG Conundrum

General Motors made a lot of noise Aug. 11 with the announcement of a 230-mile-per-gallon city fuel-economy rating for its Chevrolet Volt extended-range electric car. Not to be outdone, Nissan (NSANY) said its Leaf electric car gets an equivalent of 367 MPG.

This one-upsmanship by the two automakers probably just confused any would-be buyers of these cars, which will both hit the market later next year. It also raises serious questions for the government and car companies: How will federal regulators rate the efficiency of the newest-tech cars, and how will the automakers use that data to market them? Neither number is likely to match up the real fuel-economy performance for either car, since Volt buyers will all drive it differently and Leaf drivers won't even use gasoline.

To see how unhinged MPG becomes as electricity takes a bigger role under the hood, look at the Chevy Volt. The Volt will always drive using its electric motor and will only employ a small gasoline engine to recharge the vehicle's 400-pound, 16-kilowatt battery. In the city, where the car uses its braking system in stop-and-go traffic to recharge the battery, the Volt will almost never need the gasoline engine. Because the Volt can go 40 miles before needing a charge, the 60% of drivers who cover less than 30 miles a day may never use the gasoline engine. "For some people, the fuel economy could be infinite," says James N. Hall, principal of 2953 Analytics, a Detroit-area consulting firm.
City vs. Highway Mileage

Still, the Volt may use some gasoline in city driving, so the government's methodology gives it a 230 MPG city rating. But out on the highway, a Volt driver may use less braking and may floor the accelerator. And when they run the air conditioner, the battery drains even faster, requiring even more gas-engine recharging. GM insiders say the Volt could get less than 50 MPG under those conditions. At the moment, it looks like the Volt will be assigned a combined city/highway rating of 124 MPG, though the feds haven't certified any of these ratings yet. But how will carmakers get that across in advertising, while alerting shoppers that some of them will do far worse, and some much better? link....