bradley emmanuel

General Motors Co., eager to shift attention from its near-collapse and racing to dump its image as a maker of petrol-sucking trucks and SUVs, stoked international debate yesterday by saying it expects its upcoming Volt to get an unprecedented fuel economy rating of 230 miles per gallon (nearly 100 kilometres per litre) in city driving. That's four times better than the gas mileage of Toyota Motor Corp.'s bestselling Prius.

"Is it hooey? Probably not," said Paul Lacy, a specialist in vehicle power components with consultancy IHS Global Insight in Detroit.

"But it's likely that a good portion of us wouldn't [get that mileage]. For somebody like me, who can literally drive out of their house and get on the freeway all the way to work, you're really talking quite a bit less."

That's because some of the energy powering the Volt's lithium-ion battery will come from braking, which is generated in stop-and-start city traffic. The car is designed to operate on battery power for the first 40 miles (64 km) of driving, after which a small gasoline engine kicks in to help power the car.

Drive longer than 64 km and you use more gasoline. Add cargo and the fuel efficiency drops even further.