HAGERSTOWN, MD — Volvo’s Mack Trucks division stands to receive $3.5 million from the federal government to build four prototype diesel-electric hybrid vehicles for the Air Force, according to the Associated Press. The project would expand on $6.8 million of federally funded work Mack has done during the past three years at its engine-and-transmission plant in Hagerstown, which produced a hybrid aircraft-refueling truck that is now being tested. The funding has received Senate approval as part of the 2006 defense appropriations bill, which still needs full congressional approval. Mack’s development of more fuel-efficient, less-polluting defense vehicles would include two garbage trucks and two other trucks, possibly dump trucks, according to the Associated Press. Although they would be designed for military use, Mack hopes to apply the hybrid technology to commercial refuse trucks.