Medium- and heavy-duty trucks, motor coaches, and transit buses - collectively 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 report comprises the first periodic, five-year follow-on to the 2010 report, Technologies and Approaches to Reducing the Fuel Consumption of Medium-and Heavy-Duty Vehicles. It reviews NHTSA fuel consumption regulations and considers the technological, market and regulatory factors that may be of relevance to a revised and updated regulatory regime taking effect for model years 2019-2022.