General Motors Corp.'s 2005 lineup will begin showing hybrid vehicles at retail, but a bus fleet with GM hybrid technology is already being delivered. What if the nine largest U.S. cities replaced their 13,000 conventional buses with versions using hybrid power plants? More than 40 million gallons of fuel would be saved annually, says GM. The occasion for that estimate: lasts month's delivery of a fleet of 235 GM hybrid-equipped buses to Seattle's King County Transit Authority. The fleet, which represents the biggest single order for hybrid buses yet, teams GM's hybrid technology with a chassis built by New Flyer of Winnipeg, Manitoba, and diesel engines from Caterpillar Inc. GM calculates the Seattle fleet's annual fuel savings potential at more than 750,000 gallons, but other benefits also contribute to a compelling case for hybrids, says Detroit-based Tom Stephens, group vice president GM Power Train. "In addition to delivering a 60% improvement in fuel economy, the smaller internal combustion engines used in hybrid systems also help minimize emissions." He also credits the hybrid power system with boosting the acceleration rate by 50%. Stephens says hybrid technology also improves operating characteristics to make the bus experience more pleasant for passengers and bystanders alike. "Electrically assisted starts are smooth and quiet, without the increased diesel engine rpm and torque converter noise of conventional power trains." In the hybrid vehicle concept, the energy released in braking is no longer simply dissipated as heat. It's recovered and stored in a nickel metal hydride battery for use during acceleration. The operating characteristics of hybrids also permit longer oil change intervals for the diesel engine and transmission because the battery-powered propulsion mode automatically prevents oil-damaging overloads. The next stage of GM's hybrid strategy comes into play with the 2005 lineup. Both the Chevrolet Silverado and the GMC Sierra pickups will have hybrid versions. Stephens says hybrid offerings for 2006 will be expanded with the Chevrolet Malibu and a sport utility -- the Saturn Vue. For 2008, GM will target fuel economy gains of 25%-35% by enhancing its hybrid approach with features such as displacement-on-demand. Stephens says such systems will be introduced first on the Chevy Tahoe and the GMC Yukon.