This Final Environmental Impact Statement (FEIS) analyzes the environmental impacts of fuel consumption standards and reasonable alternative standards for model years 2014-2018 commercial medium- and heavy duty on-highway vehicles and work trucks ("HD vehicles") that NHTSA has proposed under the Energy Independence and Security Act of 2007 (EISA). Environmental impacts analyzed in this EIS include those related to fuel and energy use, air quality, and climate change. In developing these proposed standards and alternatives, NHTSA was guided by EISA, which requires that the program be "designed to achieve the maximum feasible improvement" and that the various required aspects of the program be "appropriate, cost-effective, and technologically feasible" for HD vehicles. The proposed standards would be tailored to each of three regulatory categories of HD vehicles: combination tractors; pick-up trucks and vans; and vocational trucks, as well as gasoline and diesel HD vehicle engines. The joint proposed rulemaking is consistent with the President's May 2010 directive to improve the fuel efficiency of and reduce GHG pollution from HD vehicles through coordinated Federal standards.