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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035. Washington, DC: The National Academies Press. doi: 10.17226/26092.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035. Washington, DC: The National Academies Press. doi: 10.17226/26092.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035. Washington, DC: The National Academies Press. doi: 10.17226/26092.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035. Washington, DC: The National Academies Press. doi: 10.17226/26092.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035. Washington, DC: The National Academies Press. doi: 10.17226/26092.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035. Washington, DC: The National Academies Press. doi: 10.17226/26092.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035. Washington, DC: The National Academies Press. doi: 10.17226/26092.
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Page viii Cite
Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035. Washington, DC: The National Academies Press. doi: 10.17226/26092.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035. Washington, DC: The National Academies Press. doi: 10.17226/26092.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035. Washington, DC: The National Academies Press. doi: 10.17226/26092.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035. Washington, DC: The National Academies Press. doi: 10.17226/26092.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Prepublication Copy – Subject to Further Editorial Correction Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy—2025-2035 Committee on Assessment of Technologies for Improving Fuel Economy of Light-Duty Vehicles—Phase 3 Board on Energy and Environmental Systems Division on Engineering and Physical Sciences A Consensus Study Report of PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION

THE NATIONAL ACADEMIES PRESS 500 Fifth Street, NW Washington, DC 20001 This activity was supported by Award No. DTNH2217H00028 of the U.S. Department of Transportation and National Highway Traffic Safety Administration. Any opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the views of any organization or agency that provided support for the project. International Standard Book Number-13: 978-0-309-XXXXX-X International Standard Book Number-10: 0-309-XXXXX-X Digital Object Identifier: https://doi.org/10.17226/26092 Additional copies of this publication are available from the National Academies Press, 500 Fifth Street, NW, Keck 360, Washington, DC 20001; (800) 624-6242 or (202) 334-3313; http://www.nap.edu. Copyright 2021 by the National Academy of Sciences. All rights reserved. Printed in the United States of America Suggested citation: National Academies of Sciences, Engineering, and Medicine. 2021. Assessment of Technologies for Improving Fuel Economy of Light-Duty Vehicles—2025-2035. Washington, DC: The National Academies Press. https://doi.org/10.17226/26092. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION

The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, nongovernmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Marcia McNutt is president. The National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. John L. Anderson is president. The National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president. The three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. The National Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine. Learn more about the National Academies of Sciences, Engineering, and Medicine at www.nationalacademies.org. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION

Consensus Study Reports published by the National Academies of Sciences, Engineering, and Medicine document the evidence-based consensus on the study’s statement of task by an authoring committee of experts. Reports typically include findings, conclusions, and recommendations based on information gathered by the committee and the committee’s deliberations. Each report has been subjected to a rigorous and independent peer-review process and it represents the position of the National Academies on the statement of task. Proceedings published by the National Academies of Sciences, Engineering, and Medicine chronicle the presentations and discussions at a workshop, symposium, or other event convened by the National Academies. The statements and opinions contained in proceedings are those of the participants and are not endorsed by other participants, the planning committee, or the National Academies. For information about other products and activities of the National Academies, please visit www.nationalacademies.org/about/whatwedo. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION

COMMITTEE ON ASSESSMENT OF TECHNOLOGIES FOR IMPROVING FUEL ECONOMY OF LIGHT-DUTY VEHICLES—PHASE 3 GARY MARCHANT, Arizona State University, Chair CARLA BAILO, Center for Automotive Research RODICA BARANESCU, NAE,1 University of Illinois, Chicago (retired) (resigned September 2020) NADY BOULES, NB Motors, LLC DAVID L. GREENE, University of Tennessee, Knoxville (resigned March 2021) DANIEL KAPP, D.R. Kapp Consulting, LLC ULRICH KRANZ, Canoo THERESE LANGER, American Council for an Energy-Efficient Economy ZHENHONG LIN, Oak Ridge National Laboratory JOSHUA LINN, University of Maryland, College Park NIC LUTSEY, International Council on Clean Transportation JOANN MILLIKEN, Independent Consultant, Alexandria, Virginia RANDA RADWAN, Highway Safety Research Center, University of North Carolina, Chapel Hill ANNA STEFANOPOULOU, University of Michigan and Automotive Research Center DEIDRE STRAND, Wildcat Discovery Technologies KATE WHITEFOOT, Carnegie Mellon University Staff ELIZABETH ZEITLER, Senior Program Officer, Board on Energy and Environmental Systems (BEES), Study Director K. JOHN HOLMES, Director, BEES REBECCA DeBOER, Research Assistant, BEES MICHAELA KERXHALLI-KLEINFIELD, Research Associate, BEES KATHERINE KORTUM, Senior Program Officer, Transportation Research Board BRENT HEARD, Associate Program Officer, BEES (beginning January 2020) KASIA KORNECKI, Associate Program Officer, BEES (beginning February 2020) CATHERINE WISE, Associate Program Officer, BEES (beginning June 2020) BEN WENDER, Senior Program Officer, BEES (until December 2019) HEATHER LOZOWSKI, Financial Business Partner, BEES NOTE: See Appendix B, Disclosure of Conflict(s) of Interest. 1 Member, National Academy of Engineering. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION v

BOARD ON ENERGY AND ENVIRONMENTAL SYSTEMS JARED COHON, NAE,1 Carnegie Mellon University, Chair VICKY BAILEY, Anderson Stratton Enterprises CARLA BAILO, Center for Automotive Research W. TERRY BOSTON, NAE, GridLiance GP, LLC, and Grid Protection Alliance DEEPAKRAJ DIVAN, NAE, Georgia Institute of Technology MARCIUS EXTAVOUR, XPRIZE TJ GLAUTHIER, TJ Glauthier Associates, LLC NAT GOLDHABER, Claremont Creek Ventures DENISE GRAY, LG Chem Michigan, Inc. JOHN KASSAKIAN, NAE, Massachusetts Institute of Technology BARBARA KATES-GARNICK, Tufts University DOROTHY ROBYN, Boston University KELLY SIMS GALLAGHER, The Fletcher School, Tufts University JOSÉ SANTIESTEBAN, NAE, ExxonMobil Research and Engineering Company ALEXANDER SLOCUM, NAE, Massachusetts Institute of Technology JOHN WALL, NAE, Cummins, Inc. (retired) ROBERT WEISENMILLER, California Energy Commission (former) Staff K. JOHN HOLMES, Director/Scholar HEATHER LOZOWSKI, Financial Manager REBECCA DeBOER, Program Assistant MICHAELA KERXHALLI-KLEINFIELD, Research Assistant BEN A. WENDER, Senior Program Officer (until December 2019) ELIZABETH ZEITLER, Senior Program Officer BRENT HEARD, Associate Program Officer (beginning January 2020) KASIA KORNECKI, Associate Program Officer (beginning February 2020) CATHERINE WISE, Associate Program Officer (beginning June 2020) JAMES ZUCCHETTO, Senior Scientist 1 Member, National Academy of Engineering. PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION vi

Preface Passenger car and truck manufacturers have faced corporate average fuel economy standards since 1978, and greenhouse gas emissions standards since 2012, governed by several statutes, and specified in regulations from the U.S. Department of Transportation’s National Highway Traffic Safety Administration (NHTSA) and the U.S. Environmental Protection Agency (EPA). Over this period, vehicle efficiency technology has advanced dramatically, including improvements to internal combustion engine powertrains, introductions of efficient hybrid, electric, and fuel cell vehicles, improvements to vehicle aerodynamics and mass reduction technologies, and introduction of limited vehicle automation. NHTSA and EPA have increasingly incorporated technology analysis into estimate costs and benefits of fuel economy and greenhouse gas standards. Beginning in 2007, Congress requested that the National Academies undertake periodic review of technologies for fuel economy standards. Most recently, NHTSA contracted with the National Academies to form the Committee on Assessment of Technologies for Improving Fuel Economy of Light-Duty Vehicles – Phase 3, to update the requested technology, consumer behavior, and policy analysis of vehicle efficiency technologies for 2025-2035. The committee was asked to assess technologies for improving the fuel economy of light-duty vehicles in 2025-2035, and to provide updated estimates of the potential cost, fuel economy improvements, and barriers to deployment of these technologies. The committee was asked to consider internal combustion engine, electric, and fuel cell propulsion systems, nonpowertrain technologies, the structure of the fuel economy regulations related to new technologies, shifts in personal transportation and vehicle ownership models, and consumer behavior associated with new efficiency technologies. The committee comprised a wide array of backgrounds and sought input from agency officials, vehicle manufacturers, equipment suppliers, consultants, non-governmental organizations, academicians, and many other experts. In addition to regular committee meetings, committee members held webinars on several critical topics, spoke in public sessions with experts in state and federal government, and conducted numerous information-gathering site visits to automobile manufacturers and suppliers. The committee put great effort into thorough preparation for these meetings, asked probing questions and requested follow-up information in order to understand the perspectives of the many stakeholders. In addition, the committee commissioned a material substitution and mass reduction study from the Center for Automotive Research in order to better understand the opportunities for these advances. I greatly appreciate the considerable time and effort contributed by the committee’s individual members throughout our information gathering process, report writing, and deliberations, and especially for persevering through the challenges presented by the COVID-19 pandemic during the important final stages of completing our report. The committee operated under the auspices of the National Academies of Sciences, Engineering and Medicine Board on Energy and Environmental Systems, in collaboration with the Transportation Research Board. I would like to recognize the study staff for organizing and planning meetings, and assisting with information gathering and report development. The efforts of our hard-working and knowledgeable study director Elizabeth Zeitler, ably assisted by her National Academies colleagues Rebecca DeBoer, Michaela Kerxhalli-Kleinfield, Brent Heard, Kasia Kornecki, Catherine Wise, K. John Holmes, and Katherine Kortum, were critical to the committee’s delivery of its report. I would also like to recognize Ben Wender, and Janki Patel for their early input. Thanks are also due to the many experts and presenters, too numerous to name individually, who contributed to the committee’s data-gathering process. Their contributions were invaluable and are listed in Appendix C. Gary Marchant, Chair, Committee on Assessment of Technologies for Improving Fuel Economy of Light-Duty Vehicles – Phase 3 PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION vii

Acknowledgment of Reviewers This Consensus Study Report was reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise. The purpose of this independent review is to provide candid and critical comments that will assist the National Academies of Sciences, Engineering, and Medicine in making each published report as sound as possible and to ensure that it meets the institutional standards for quality, objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We thank the following individuals for their review of this report: GEORGE CRABTREE, NAS,1 Argonne National Laboratory Joint Center for Energy Storage Research PATRICK DAVIS, Strategic Marketing Innovations DANIEL GASPAR, Pacific Northwest National Laboratory CHRIS GEARHART, National Renewable Energy Laboratory KENNETH GILLINGHAM, Yale University ROY GOUDY, Nissan Technical Center North America CHRIS HENDRICKSON, NAE,2 Carnegie Mellon University ASHLEY HORVAT, Greenlots JEREMY MICHALEK, Carnegie Mellon University MARGE OGE, U.S. Environmental Protection Agency (ret.) GREG PANNONE, IHS Markit HUEI PENG, University of Michigan GIORGIO RIZZONI, The Ohio State University GARY W. ROGERS, Roush Enterprises KRISTIN SLANINA, TrueCar GUI-JIA SU, Oak Ridge National Laboratory RICHARD YEN, Altair Although the reviewers listed above provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations of this report nor did they see the final draft before its release. The review of this report was overseen by Susan Hanson, Clark University, and Andrew Brown Jr., Diamond Consulting, Engineering, & Management Services. They were responsible for making certain that an independent examination of this report was carried out in accordance with the standards of the National Academies and that all review comments were carefully considered. Responsibility for the final content rests entirely with the authoring committee and the National Academies. 1 Member, National Academy of Sciences 2 Member, National Academy of Engineering PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION viii

Contents SUMMARY S-1 1 INTRODUCTION 1-1 1.1 A Snapshot of Today’s LDV Fleet 1.2 A Look at the Future 1.3 Light-Duty Vehicle System Energy Use 1.4 Context for Fuel Economy Improvements 1.5 Statement of Task 1.6 References 2 FUEL ECONOMY, GHG EMISSIONS, AND VEHICLE EFFICIENCY BACKGROUND 2-12 2.1 Technology Principles Affecting Vehicle Efficiency 2.2 Fuel Consumption, GHG Emissions, and Energy Use 2.3 Technical, Regulatory and Statutory History 2.4 Test Cycle and Real World Fuel Economy 2.5 References 3 2025 BASELINE OF VEHICLES 3-25 3.1 Comparative Benchmarks for 2016-2026 Vehicles 3.2 Baseline Vehicle Classes 3.3 Future Year CO2 Reduction and Increased Efficiency to 2025 3.4 Model Year 2020 Vehicles with Lowest CO2 Emissions 3.5 Benchmark for Model Years 2025 and 2026 3.6 Benchmark for Model Year 2025 3.7 Technology Packages in 2025 3.8 International Market and Regulations 3.9 References 4 INTERNAL COMBUSTION ENGINE BASED POWERTRAIN TECHNOLOGIES 4-40 4.1 Downsized/Boosted ICE Pathway 4.2 Naturally Aspirated ICE Pathway 4.3 Compression Ignition Diesel Engines 4.4 Transmission Pathway 4.5 Hybridized Powertrain Pathway 4.6 Advanced Combustion Technologies 4.7 References 5 BATTERY ELECTRIC VEHICLES 5-77 5.1 Introduction 5.2 The Electric Drive 5.3 Batteries for Electric Vehicles 5.4 Electric Charging Infrastructure 5.5 Summary of Electric Vehicle Costs PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION ix

5.6 References 6 FUEL CELL ELECTRIC VEHICLES 6-157 6.1 Background 6.2 Fuel Cell Basics 6.3 FCEV Current Status and Planned Developments 6.4 FCEV Technology R&D 6.5 Hydrogen Refueling Infrastructure for FCEVs 6.5 Summary of Fuel Cell Vehicle Costs 6.6 Findings and Recommendations for Fuel Cell Electric Vehicles 6.7 References 7 NON-POWERTRAIN TECHNOLOGIES 7-225 7.1 Aero 7.2 Mass Reduction 7.3 Tires 7.4 Accessories and Other Off-Cycle Technologies 7.5 Considerations for Mass and Safety in Light of Increased Penetration of ADAS and xEV 7.6 Total Opportunities for Road Load and Accessory Power Draw Reduction 7.7 References 8 CONNECTED AND AUTOMATED VEHICLES 8-265 8.1 Introduction 8.2 Connected and Automated Vehicle Technologies 8.3 Impacts of CAV Technologies on Vehicle Efficiency 8.4 Estimates of Fuel Efficiency Effects 8.5 Policy Issues Related to CAV Energy Impacts 8.6 References 9 AUTONOMOUS VEHICLES 9-303 9.1 Introduction 9.2 Vehicle Miles Traveled 9.3 Vehicle Ownership Models 9.4 Vehicle Characteristics 9.5 Relationships among Autonomy, Connectivity, Sharing, and Electrification of Vehicles 9.6 Combined Energy Impacts of Autonomous Vehicles 9.7 Autonomous Vehicles and Energy Use: Policy Issues 9.8 Findings and Recommendations 9.9 References 10 ENERGY AND EMISSIONS IMPACTS OF NONPETROLEUM FUELS IN LIGHT-DUTY 10-319 VEHICLE PROPULSION 10.1 Introduction 10.2 Electricity, Hydrogen and Low-Carbon Synthetic Fuels 10.3 Low-Carbon Fuels in the 2025-2035 Fleet 10.4 Recommendations for Non-Petroleum Fuels 10.5 References 11 CONSUMER ACCEPTANCE AND MARKET RESPONSE TO STANDARDS 11-343 11.1 Historical Market Trends 11.2 Fuel Economy and Vehicle Travel: Rebound Effects PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION x

11.3 How Much Do Consumers Value Fuel Cost Savings and What Are the Implications for Benefit-Cost Analysis? 11.4 Transitions to New Technology 11.5 The Role of EV Incentives, the Impact of Incentive Expiration and the Recommendation Whether to Continue EV Incentives 11.6 References 12 REGULATORY STRUCTURE AND FLEXIBILITIES 12-379 12.1 History of Vehicle Fuel Economy Regulation 12.2 Measuring Fuel Economy and GHG Emissions 12.3 Regulatory Flexibilities 12.4 International Context of Regulatory Environment 12.5 Fuel Economy Regulation in a Warming World 12.6 References 13 EMERGENT FINDINGS, RECOMMENDATIONS, AND FUTURE POLICY 13-414 SCENARIOS FOR CONTINUED REDUCTION IN ENERGY USE AND EMISSIONS OF LIGHT-DUTY VEHICLES 13.1 Emergent Findings and Recommendations 13.2 Big Picture: Rethinking Regulation of Fuel Economy in 2025-2035 and Beyond APPENDIXES A Committee Biographical Information A-430 B Disclosure of Conflicts of Interest B-436 C Committee Activities C-437 D Acronyms D-442 E Summary of Center for Automotive Research Study E-449 PREPUBLICATION COPY—SUBJECT TO FURTHER EDITORIAL CORRECTION xi

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From daily commutes to cross-country road trips, millions of light-duty vehicles are on the road every day. The transportation sector is one of the United States’ largest sources of greenhouse gas emissions, and fuel is an important cost for drivers. The period from 2025-2035 could bring the most fundamental transformation in the 100-plus year history of the automobile. Battery electric vehicle costs are likely to fall and reach parity with internal combustion engine vehicles. New generations of fuel cell vehicles will be produced. Connected and automated vehicle technologies will become more common, including likely deployment of some fully automated vehicles. These new categories of vehicles will for the first time assume a major portion of new vehicle sales, while internal combustion engine vehicles with improved powertrain, design, and aerodynamics will continue to be an important part of new vehicle sales and fuel economy improvement.

This study is a technical evaluation of the potential for internal combustion engine, hybrid, battery electric, fuel cell, nonpowertrain, and connected and automated vehicle technologies to contribute to efficiency in 2025-2035. In addition to making findings and recommendations related to technology cost and capabilities, Assessment of Technologies for Improving Light-Duty Vehicle Fuel Economy - 2025-2035 considers the impacts of changes in consumer behavior and regulatory regimes.

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