The prospects for hybrid electric vehicles were bolstered on Monday when General Motors and DaimlerChrysler, two automakers long skeptical about hybrids, said they would develop them by working together.
The two companies have already been separately developing hybrids and said they had been in discussions since last year. They agreed to jointly develop a compact hybrid system that saves gas both on the highway and in the city, where today's hybrids are more efficient. It will also be designed for full-size trucks and for use with diesels and gasoline engines.
The companies said their first vehicles would not be on the road until 2007.
Eric Ridenhour, executive vice president of product development at Daimler's Chrysler division, likened current hybrid technology to videocassettes.
"We like to think of this as the DVD or streaming video, the whole next way of doing it," he said.
Tom Stephens, a GM group vice president, said the new system would "achieve at least a 25 percent improvement" in overall fuel economy in large trucks, without compromising how much they could tow.
Competitors, however, were skeptical about the value of the advances.
"The Escape hybrid today gets a 50 percent combined fuel economy improvement and 80 percent in city driving," said Jon Harmon, a spokesman for Ford Motor, which introduced a hybrid version of its Escape sport utility vehicle this year. "So I'm not sure what the leapfrog is in a 25 percent improvement."
GM makes a hybrid system for buses, and both GM and Daimler are selling a small number of pickups that use a mild form of hybrid technology to improve fuel economy 10 percent or more.
Hybrids made by Honda, Toyota and Ford offer fuel savings of 40 percent or more -- and potentially much more, depending on how and where the vehicles are driven.
GM has said that by 2007 it will offer a more ambitious hybrid system in its Chevrolet Tahoe and GMC Yukon sport utility vehicles. On Monday, it said those two vehicles would be the first to use the co-developed system.
Daimler's Chrysler division said it would follow GM in late 2007 or early 2008 with a hybrid of its Dodge Durango SUV.