INTRODUCTION Medium- and heavy-duty (MDHD) trucks (Classes 2b - 8) consume approximately 20% of U.S. transportation fuel and emit 20% of vehicle-related greenhouse gases (GHGs) [ 1]. As a result of the significant contribution to overall GHGs from MDHD vehicles in the U.S., the National Highway Traffic Safety Administration (NHTSA) and the United States Environmental Protection Agency (EPA) finalized regulations to reduce fuel consumption and GHG emissions from medium- and heavy-duty trucks in 2011 [ 1]. Phase 1 of this program affects model years 2014 to 2018 vehicles. The agencies are currently working on a proposal for Phase 2 [ 2]. To support the development of standards for Phase 2, NHTSA sponsored research at Southwest Research Institute (SwRI) to assess the technical feasibility of reducing MDHD vehicle fuel consumption. This paper summarizes results for the heavy-duty long haul combination tractor-trailer segment of the SwRI analysis. Detailed results from the analysis can be found in SwRI's 2015 report to NHTSA, along with a detailed assessment of a class 2b/3 pickup and of two Class 5 and 6 vocational trucks [ 3]. Figure 1 shows that tractor-trailer vehicle fuel use and CO2 emissions represents about two thirds of the MDHD total. The specific vehicle simulated in this study is a sleeper cab combination tractor, which represents 39% of the total fuel use. In 2011, all tractor types (high-, mid- and low-roof sleepers, and day cabs) represented about 10% of the MDHD trucks sold that year. Over 98% of combination tractor-trailer vehicles are powered by diesel engines, with the remainder being powered by natural gas. Figure 1. MDHD CO2 Emissions by Vehicle Category [ 15] Studies published prior to the release of the Phase 1 regulation, such as a National Academy of Sciences 2010 report [ 4] and TIAX [ 5], reported that up to 50% of tractor-trailer fuel consumption can be eliminated with engine and vehicle improvements, compared to a 2009 vehicle baseline. The 50% fuel savings figure includes technologies not considered in this study, such as hybrid systems and Heavy-Duty Vehicle Fuel Saving Technology Analysis to Support Phase 2 Regulations Nicholas Badain and Thomas Reinhart Southwest Research Institute Coralie Cooper DOT/V olpe Center James MacIsaac and John Whitefoot National Highway Traffic Safety Admin. ABSTRACT This paper presents the fuel consumption results of engine and vehicle simulation modeling for a wide variety of individual technologies and technology packages applied to a long haul heavy duty vehicle. Based on the simulation modeling, up to 11% in fuel savings is possible using commercially available and emerging technologies applied to a 15L DD15 engine alone. The predicted fuel savings are up to 17% in a Kenworth T700 tractor-trailer unit equipped with a range of vehicle technologies, but using the baseline DD15 diesel engine. A combination of the most aggressive engine and vehicle technologies can provide savings of up to 29%, averaged over a range of drive cycles. Over 30% fuel savings were found with the most aggressive combination on a simulated long haul duty cycle. Note that not all of these technologies may prove to be cost-ef fective. The fuel savings benefits for individual technologies vary widely depending on the drive cycles and payload. CITATION: Badain, N., Reinhart, T., Cooper, C., MacIsaac, J. et al., "Heavy-Duty Vehicle Fuel Saving Technology Analysis to Support Phase 2 Regulations," SAE Int. J. Commer. Veh. 8(2):2015, doi:10.4271/2015-01-2775.2015-01-2775 Published 09/29/2015 Copyright © 2015 SAE International doi:10.4271/2015-01-2775 saecomveh.saejournals.org 419controls features that provide driver management and coaching. This analysis provides an updated study of potential savings using a 2019 vocational vehicle baseline. The technologies evaluated in this study were selected by SwRI and NHTSA with input from EPA and other organizations. Ce