General Motors is taking a step forward in the race to produce green cars with an announcement today that it has developed a new concept vehicle, called the Triax, that can operate with a range of power sources, including gasoline, hybrid, and electric systems powered by either batteries or fuel cells. In the meantime, U.S. automakers are planning to install more efficient, cleaner engines in some of their trucks, replacing old V-6 and V-8 systems. They will try to convince consumers that the new engines will still pack a powerful punch. The EPA has proposed new regulations that would force automakers to reduce emissions from light trucks, and the agency is considering expanding the requirements to cover even the biggest pickups and SUVs.