A new generation of hybrid diesel prototypes being developed by General Motors, DaimlerChrysler and Ford will offer new choices in fuel-sipping vehicles, according to a report on Wired.com. Diesel hybrid technology is already being used in large vehicles that transport heavy loads, including buses and locomotives, according to the report. General Motors subsidiary Allison Transmission produces hybrid diesel engines used by several municipal bus services. Diesel and hybrid technologies have synergies, said Charlie Freese, executive engineering director at GM Powertrain. Hybrid systems reduce fuel consumption by relying on the electric motor while idling and during acceleration of stop-and-go traffic. Diesel engines are optimized for hauling heavy loads and for steady-speed highway driving. Earlier this year, GM unveiled the Opel Astra Diesel Hybrid, a sedan concept vehicle the company claims would increase fuel economy by 25 percent over a comparable diesel car, or approximately 59 miles per gallon. The vehicle uses a hybrid system with two electric motors being co-developed with DaimlerChrysler, according to GM. DaimlerChrysler produced 100 Dodge Ram hybrid electric vehicle diesel pickup trucks in December. DaimlerChrysler's future diesel hybrids will be based on the hybrid technology being developed with GM and would be available in late 2007 or early 2008, according to spokesman Cole Quinnell. Automakers are more likely to offer diesel hybrids in Europe before the United States gets them because diesel fuel is much more expensive there. And diesel vehicles have a much higher market penetration there, according to Benjamin. Integrating both hybrid and diesel technology could add up to $8,000 to the price of a vehicle, which may limit its appeal to American consumers. "Even (with gas at) $3 a gallon, $8,000 (more) is a lot to pay." Meeting California's tougher emissions requirements, which have been adopted by four other states, may present more of a challenge.