A fleet of hybrid-electric buses will save the Seattle area 750,000 gallons of fuel yearly. This, according to General Motors Corp. which will equip 235 buses with hybrid technology that is claimed to boost fuel economy up to 60%. The fuel savings are said to be equivalent to replacing 8,000 internal-combustion engine vehicles with hybrid-electric vehicles. The hybrid buses will produce 90% fewer particulates, hydrocarbons and carbon-monoxide emissions, and 60% fewer oxides of nitrogen than the buses they replace.

"General Motors' hybrid strategy focuses on first applying the technology to the highest fuel-consuming vehicles, such as transit buses, full-size pickup trucks, and sport-utility vehicles," says Tom Stephens, group vice president of GM Powertrain. "For example, replacing the 13,000 buses operating in the nine largest transit markets in the U.S. with our hybrid technology would bring annual savings of more than 40 million gallons of fuel, equivalent to more than a half million small hybrid passenger cars."

The hybrid-electric bus uses two power sources -- an engine and battery. The engine-generator works in parallel with the battery, providing electric power for battery charging. The engine links to a drive unit that delivers a continuously variable ratio of power to the wheels. The diesel engine's mechanical power maintains speed after the vehicle is moving. A lightweight nickel-metal hydride battery weighs one-third less and is one-half the size of a conventional lead-acid system. Lead-acid batteries have less than two years of life while NiMH batteries are said to last six years.