Medium- and heavy-duty trucks, motor coaches, and transit buses - collectively, "medium- and heavy-duty vehicles", or MHDVs - are used in every sector of the economy. The fuel consumption and greenhouse gas emissions of MHDVs have become a focus of legislative and regulatory action in the past few years. This study is a follow-on to the National Research Council's 2010 report, Technologies and Approaches to Reducing the Fuel Consumption of Medium-and Heavy-Duty Vehicles. That report provided a series of findings and recommendations on the development of regulations for reducing fuel consumption of MHDVs. On September 15, 2011, NHTSA and EPA finalized joint Phase I rules to establish a comprehensive Heavy-Duty National Program to reduce greenhouse gas emissions and fuel consumption for on-road medium- and heavy-duty vehicles. As NHTSA and EPA began working on a second round of standards, the National Academies issued another report, Reducing the Fuel Consumption and Greenhouse Gas Emissions of Medium- and Heavy-Duty Vehicles, Phase Two: First Report, providing recommendations for the Phase II standards. This third and final report focuses on a possible third phase of regulations to be promulgated by these agencies in the next decade. Table of Contents Front Matter Summary 1 Introduction 2 Setting the Stage: Regulatory Horizons, Challenges, and Influences 3 Certification, Compliance, and Enforcement 4 Powertrain Technologies 5 Technologies for Reducing the Power Demand of MHDVs 6 Projected Benefits of Technologies on Fuel Consumption 7 Hybrid and Electric Powertrain Technologies 8 Battery Technology for Medium- and Heavy-Duty Hybrid and Electric Vehicles 9 Freight Operational Efficiency 10 Intelligent Transportation Systems and Automation 11 Manufacturing Considerations 12 Costs and Benefits 13 Alternative and Complementary Regulatory Approaches Appendix A: Committee Biographies Appendix B: Disclosure of Conflicts of Interest Appendix C: Committee Activities Appendix D: Summary of Analysis of Engine and Vehicle Combinations Appendix E: Description of Drive Cycles Used for Compliance Appendix F: Summary of Committee's First Report: Reducing the Fuel Consumption and Greenhouse Gas Emissions of Medium- and Heavy-Duty Vehicles, Phase Two: First Report Appendix G: Acronyms and Abbreviations Autorid: National Academies of Sciences, Engineering, and Medicine, Transportation Research Board, Division on Engineering and Physical Sciences, Board on Energy and Environmental Systems, Committee on Assessment of Technologies and Ap