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.

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