DETROIT -- General Motors Corp.'s advanced hybrid technology will be used on transit buses in the Seattle area beginning in June, eventually creating the nation's largest fleet of diesel-electric hybrid buses, according to The Associated Press. The 235 new buses will account for about 15 percent of King County Metro Transit's 1,300-vehicle fleet. Sound Transit Regional Express also will use the new vehicles. The 60-foot mass-transit vehicles, which are more expensive than standard diesel buses, deliver up to 60 percent greater fuel economy and can reduce emissions by as much as 90 percent, GM said. County transit officials say they expect the hybrid buses to save roughly 750,000 gallons of fuel a year. King County secured $5 million in federal funding to help pay for the new buses, which the county has said have a price tag of $645,000 each -- $200,000 more than a standard bus. The first group of the hybrid buses was scheduled to join the fleet June 5. GM says the remainder will be delivered by year's end. New Flyer of Winnipeg, Manitoba manufactures the buses, which use diesel engines supplied by Caterpillar Inc. Already, Orange County, Calif., and Philadelphia are among the places using GM hybrid technology on transit buses. GM said more orders are pending.