The Environmental Protection Agency (EPA) and the National Highway Traffic Safety Administration (NHTSA), on behalf of the Department of Transportation, are each adopting rules to establish a comprehensive Heavy-Duty National Program that would reduce greenhouse gas emissions and increase fuel efficiency for on-road heavy-duty vehicles, responding to the President's directive on May 21, 2010, to take coordinated steps to produce a new generation of clean vehicles. NHTSA's fuel consumption standards and Environmental Protection Agency's (EPA's) carbon dioxide (CO2) emissions standards would be tailored to each of three regulatory categories of heavy-duty vehicles: (1) Combination Tractors; (2) Heavy-duty Pickup Trucks and Vans; and (3) Vocational Vehicles, as well as gasoline and diesel heavy-duty engines. EPA's hydrofluorocarbon emissions standards will apply to air conditioning systems in tractors, pickup trucks, and vans, and EPA's nitrous oxide (N2O) and methane (CH4) emissions standards will apply to all heavy-duty engines, pickup trucks, and vans. This Regulatory Impact Analysis (RIA) provides detailed supporting documentation to the EPA and NHTSA joint program under each of their respective statutory authorities. Because there are slightly different requirements and flexibilities in the two authorizing statutes, this RIA provides documentation for the primary joint provisions as well as for provisions specific to each agency. This RIA is generally organized to provide overall background information, methodologies, and data inputs, followed by results of the various technical and economic analyses.