United States. Congress, Energy Independence and Security Act of 2007…
“ In General— The Secretary, in consultation with the Administrator of the Environmental Protection Agency and the Secretary of Transportation, shall conduct a study of methods of increasing the fuel efficiency of vehicles using biogas by optimizing natural gas vehicle systems that can operate on biogas, including the advancement of vehicle fuel systems and the combination of hybrid-electric and plug-in hybrid electric drive platforms with natural gas vehicle systems using biogas. ”
