This rulemaking would address fuel efficiency standards for medium- and heavy-duty on-highway vehicles and work trucks for model years beyond 2018. This rulemaking would respond to requirements of the Energy Independence and Security Act of 2007 (EISA), title 1, subtitle A, sections 102 and 108, as they amend 49 USC section 32902, which was signed into law December 19, 2007. The statute requires that NHTSA establish a medium- and heavy-duty on-highway vehicle and work truck fuel efficiency improvement program that achieves the maximum feasible improvement, including standards that are appropriate, cost-effective, and technologically feasible. The law requires that the new standards provide at least 4 full model years of regulatory lead-time and 3 full model years of regulatory stability (i.e., the standards must remain in effect for 3 years before they may be amended). This action would follow the first ever Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles ("Phase 1") (76 FR 57106, September 15, 2011). In June, 2013, the President's Climate Action Plan called for the Department of Transportation to develop fuel efficiency standards and the Environmental Protection Agency to develop greenhouse gas emission standards in joint rulemaking within the President's second term. In February 2014, the President directed DOT and EPA to complete the second phase of Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles during his second term.