When the driver demands more speed, the engine turns itself on. Cruising on the highway, the gasoline engine supplies the power, so Prius has the same range and fuel supply as a straight gasoline car. For maximum acceleration, both the engine and the battery drive the wheels. The Prius, or something like it, will come to America in two years or so, Toyota says. American auto makers, who are developing their own hybrids under the industry-government Partnership for a New Generation of Vehicles, are skeptical about its prospects here.
Hybrids capture part of the braking energy to recharge the battery, increasing fuel economy.
They're less likely to show much advantage where speeds are constant. Hybrids are not likely to be shown at all in Europe, where traffic really moves. Engineers at Daimler-Benz, for example, can't understand why anyone would want to pay for two separate drivetrains in the same car. The electric drive helps a bit during acceleration, moves the car in reverse, and provides power for accessories. With the diesel engine alone, the car gets 63 miles per gallon.