Automakers have finally combined the best of two cars-the electric and the gasoline powered-into one fuel-efficient hybrid. The Honda Insight and the Toyota Prius (see animation), which arrived in U.S. showrooms in 1999 and 2000, respectively, rely primarily on gasoline, switching to electricity under light loads, or use both types of energy simultaneously when the vehicle needs a boost of power. Sensors placed throughout the car monitor conditions such as throttle position, vehicle speed, and battery charge, and relay the readings to a computer that decides how to optimally divide the load between the gasoline engine and electric motor.

Neither the Insight nor the Prius needs to be plugged in; both recharge their battery during normal operation. One clever way they accomplish this is through regenerative braking. When the driver decelerates or brakes, the motion of the slowing wheels turns the generator and creates energy that is used to recharge the battery. By using the otherwise wasted energy of braking, the hybrids get better gas mileage in the city than conventional vehicles do. The Prius averages 48 miles per gallon, the Insight, 56 mpg. Both are rated by the California Air Resources Board as being 90 percent cleaner than the average new 2002 model year car.