Toyota Motor Corp said on April 9 it plans to roll out for a test drive this summer a prototype of a new zero-emission vehicle powered by a fuel cell and a battery. The latest version of Toyota's fuel cell hybrid car will be based on a five-passenger Highlander sport-utility vehicle and run primarily on a fuel cell producing 90 kilowatts of power, up from 25 kilowatts in the previous version unveiled four years ago. Despite unresolved technical problems, Japan's largest automaker was optimistic on the outlook for fuel cell vehicles, which use hydrogen as fuel to produce electricity and are widely considered the most promising low- or no-pollution replacement for the internal combustion engine. "We might be able to get fuel-cell cars sooner than many are expecting," Toyota Managing Director Hiroyuki Watanabe told a briefing for reporters. He noted, however, that a number of issues, including cost, safety and reliability, need to be addressed before fuel cell vehicles become a common sight -- considered unlikely until 2010 or later. His optimism was based in part on the success of Toyota's Prius hybrid electric vehicle, which combines a gasoline engine with an electric motor to achieve nearly double the fuel efficiency of a conventional gasoline-engine vehicle. Toyota has sold more than 50,000 of the cars since its November 1997 launch, exceeding initial expectations, according to Watanabe. The fuel cell hybrid would replace Prius's gasoline engine with fuel-cell power. Watanabe also played down differences between DaimlerChrysler AG's fuel cell prototypes using methanol fuel, from which hydrogen is extracted, and Toyota's concept of using clean hydrocarbon fuel, which would be more easily integrated with existing fuel distribution infrastructure. "There will be various processes," Watanabe said, adding that the pursuit of several different options would help speed up the adoption of hydrogen fuel.