National Academies Press: OpenBook
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2022. Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts. Washington, DC: The National Academies Press. doi: 10.17226/26469.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2022. Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts. Washington, DC: The National Academies Press. doi: 10.17226/26469.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2022. Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts. Washington, DC: The National Academies Press. doi: 10.17226/26469.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2022. Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts. Washington, DC: The National Academies Press. doi: 10.17226/26469.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2022. Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts. Washington, DC: The National Academies Press. doi: 10.17226/26469.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2022. Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts. Washington, DC: The National Academies Press. doi: 10.17226/26469.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2022. Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts. Washington, DC: The National Academies Press. doi: 10.17226/26469.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2022. Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts. Washington, DC: The National Academies Press. doi: 10.17226/26469.
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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.

2022 N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP RESEARCH REPORT 984 Breaking Barriers ALTERNATIVE APPROACHES TO AVOIDING AND REDUCING HIGHWAY TRAFFIC NOISE IMPACTS Judith Rochat Doug Barrett Shannon McKenna Keith Yoerg Cross-Spectrum Acoustics Inc. Pasadena, CA Karel Cubick Sean Riffle Lisa Samples ms consultants, inc. Akron, OH Robert Rasmussen Richard Sohaney The Transtec Group, Inc. Austin, TX Subscriber Categories Design • Environment • Highways Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed, and implementable research is the most effective way to solve many problems facing state departments of transportation (DOTs) administrators and engineers. Often, highway problems are of local or regional interest and can best be studied by state DOTs individually or in cooperation with their state universities and others. However, the accelerating growth of highway transporta- tion results in increasingly complex problems of wide interest to high- way authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 ini- tiated an objective national highway research program using modern scientific techniques—the National Cooperative Highway Research Program (NCHRP). NCHRP is supported on a continuing basis by funds from participating member states of AASHTO and receives the full cooperation and support of the Federal Highway Administration (FHWA), United States Department of Transportation, under Agree- ment No. 693JJ31950003. The Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine was requested by AASHTO to administer the research program because of TRB’s recognized objectivity and understanding of modern research practices. TRB is uniquely suited for this purpose for many reasons: TRB maintains an extensive com- mittee structure from which authorities on any highway transportation subject may be drawn; TRB possesses avenues of communications and cooperation with federal, state, and local governmental agencies, univer- sities, and industry; TRB’s relationship to the National Academies is an insurance of objectivity; and TRB maintains a full-time staff of special- ists in highway transportation matters to bring the findings of research directly to those in a position to use them. The program is developed on the basis of research needs iden- tified by chief administrators and other staff of the highway and transportation departments, by committees of AASHTO, and by the FHWA. Topics of the highest merit are selected by the AASHTO Special Committee on Research and Innovation (R&I), and each year R&I’s recommendations are proposed to the AASHTO Board of Direc- tors and the National Academies. Research projects to address these topics are defined by NCHRP, and qualified research agencies are selected from submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Academies and TRB. The needs for highway research are many, and NCHRP can make significant contributions to solving highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement, rather than to substitute for or duplicate, other highway research programs. Published research reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet by going to https://www.mytrb.org/MyTRB/Store/default.aspx Printed in the United States of America NCHRP RESEARCH REPORT 984 Project 25-57 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-09426-9 Library of Congress Control Number 2021950994 © 2022 National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FTA, GHSA, NHTSA, or TDC endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. Cover photo caption: Typical cross-section of solid safety barriers. NOTICE The research report was reviewed by the technical panel and accepted for publication according to procedures established and overseen by the Transportation Research Board and approved by the National Academies of Sciences, Engineering, and Medicine. The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research and are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; the FHWA; or the program sponsors. The Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; and the sponsors of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers’ names or logos appear herein solely because they are considered essential to the object of the report.

The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, non- governmental 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. The Transportation Research Board is one of seven major programs of the National Academies of Sciences, Engineering, and Medicine. The mission of the Transportation Research Board is to provide leadership in transportation improvements and innovation through trusted, timely, impartial, and evidence-based information exchange, research, and advice regarding all modes of transportation. The Board’s varied activities annually engage about 8,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. Learn more about the Transportation Research Board at www.TRB.org.

C O O P E R A T I V E R E S E A R C H P R O G R A M S AUTHOR ACKNOWLEDGMENTS The researchers hope this project and research report help to expand the strategies applied to reduce highway traffic noise. The researchers thank the more than 50 individuals who participated in the literature and data review surveys and interviews. Those individuals also provided documents and data, including from the American Association of State Highway and Transportation Officials and the Transporta- tion Research Board. In addition, the researchers thank Ysbrand Wijnant and Bart Willems from the University of Twente and 4Silence in the Netherlands for providing valuable noise predictions for barrier diffractor tops. CRP STAFF FOR NCHRP RESEARCH REPORT 984 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Waseem Dekelbab, Associate Program Manager, National Cooperative Highway Research Program Ann M. Hartell, Senior Program Officer Jarrel McAfee, Senior Program Assistant Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications NCHRP PROJECT 25-57 PANEL Field of Transportation Planning—Area of Human and Natural Environment Adam T. Alexander, Gannett Fleming Inc., Tacoma, WA (Chair) Noel Alcala, Ohio Department of Transportation, Columbus, OH Patrick G. Gant, Texas Department of Transportation, Houston, TX John Robert Hencken, Rutgers University, Piscataway, NJ Mary Alice Pair, North Carolina Department of Transportation, Raleigh, NC Kenneth Donel Polcak, Maryland State Highway Administration (Retired), Baltimore, MD Peter Wasko, Minnesota Department of Transportation, St. Paul, MN Aileen Varela-Margolles, FHWA Liaison Melissa Anderson Savage, AASHTO Liaison Christine L. Gerencher, TRB Liaison

NCHRP Research Report 984: Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts presents the results of a review of innovative strate- gies to avoid and/or reduce highway noise impacts. The two-part research report includes the results of detailed modeling of the potential noise reduction from a set of promising approaches, along with a practitioner’s handbook to help identify appropriate strategies for common types of highway projects. This report will be of interest to noise practitioners at state depart- ments of transportation (DOTs) and to others who want to learn more about alternatives to noise walls for reducing highway noise impacts to communities. State DOTs are required to consider highway traffic noise impacts from projects on existing and planned facilities. When these impacts exceed certain thresholds, the Code of Federal Regu- lations 23 CFR Part 772 specifies a limited number of approaches to mitigate highway traffic noise. The most commonly used approach is noise barriers—usually noise walls. To date, some 3,000 miles of noise walls have been constructed along U.S. highways, at an average cost of $2M per mile of wall. However, noise walls are not always effective and appropriate. In some cases, a noise analysis indicates that a noise wall is not feasible and reasonable per 23 CFR Part 772. In other cases, a noise wall may provide only limited reductions of noise levels because of site conditions such as topography or local road traffic volumes. Noise reduction targets established by policy or regulation can lead to situations where a transportation agency constructs a noise wall only for those portions of a community that qualify for abatement under regulatory requirements, while other portions of the same com- munity receive no noise reduction benefit. Even if noise levels do not meet regulatory defi- nitions of a noise impact, state DOTs and other transportation agencies may also seek to address complaints of excessive highway traffic noise. In addition, some communities may want reduced highway traffic noise but oppose a noise wall. Conversely, communities may advocate for a noise barrier, although topography and other site conditions may mean that a barrier will provide little reduction in noise. The objective of NCHRP Project 25-57: “Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts” was to investigate the noise reduc- tion potential of alternative strategies to provide state DOTs with essential information about the effectiveness and feasibility of innovative approaches that can balance community interests; regulatory requirements; and policy, project context, and costs. The research explored a wide range of approaches—used alone or in combination. These included on-road design choices such as quieter pavements, bridge decks, and bridge joints; highway design choices such as adjustments to vertical or horizontal alignment; right-of-way design choices such as earthen F O R E W O R D By Ann M. Hartell Staff Officer Transportation Research Board

berms or sound-absorbing ground surfaces; and traffic management strategies such as speed or truck restrictions. Cross-Spectrum Acoustics Inc. was tasked with conducting a literature review to identify alternative strategies to avoiding and/or reducing highway traffic noise. Using the current version of the Federal Highway Administration Transportation Noise Model, the research team developed ranges of potential traffic noise reduction for a selected set of strategies. The research and modeling results are translated into a practitioner’s handbook designed to help noise specialists and highway designers identify strategies that can be effective alter- natives to noise walls based on road type, general costs, and context considerations. The practitioner’s handbook is included in this report as Part II. The handbook is accompanied by a standalone document with a set of flowcharts to guide the selection of alternative strategies. The flowcharts and a set of PowerPoint presentation slides summarizing the project are available for download from the TRB website (search for “NCHRP Research Report 984” at www.trb.org). Appendices A through E accompany Part I and are available by searching for the report at www.trb.org.

1 Summary P A R T I Conduct of Research 13 Chapter 1 Background 15 Chapter 2 Research Approach 15 2.1 Literature and Data Review 15 2.2 Further Investigations 21 Chapter 3 Findings: On-Road Design Strategies 21 3.1 Strategy Summaries 24 3.2 Detailed Investigations 25 Chapter 4 Findings: Highway Design Strategies 25 4.1 Strategy Summaries 29 4.2 Detailed Investigations – Solid Safety Barriers 50 Chapter 5 Findings: Right-of-Way Design Strategies 50 5.1 Strategy Summaries 59 5.2 Detailed Investigations – Low Berms 88 5.3 Detailed Investigations – Acoustically Soft Ground 111 Chapter 6 Findings: Operations Management Strategies 111 6.1 Strategy Summaries 112 6.2 Detailed Investigations 113 Chapter 7 Findings: Strategies Implemented by Receptors or Local Governments 113 7.1 Strategy Summaries 113 7.2 Detailed Investigations 115 Chapter 8 Findings: Sound-Absorptive Treatment Strategies 115 8.1 Strategy Summaries 118 8.2 Detailed Investigations 119 Chapter 9 Application of Findings 119 9.1 Choosing a Strategy 120 9.2 Practitioner’s Handbook 121 Chapter 10 Conclusions and Suggested Research 121 10.1 Conclusions 123 10.2 Suggested Research 128 Bibliography 135 Appendices C O N T E N T S

P A R T I I Practitioner’s Handbook 139 Chapter 11 Introduction 140 Chapter 12 Purpose of the Practitioner’s Handbook 141 Chapter 13 How to Use the Practitioner’s Handbook 143 Chapter 14 Roadway Types Versus Strategy Matrix 145 14.1 Roadway Types Versus Strategy Matrix 146 Chapter 15 Overview of Strategies That Reduce or Avoid Noise Impacts 146 15.1 On-Road Design Strategies 147 15.2 Highway Design Strategies 149 15.3 Right-of-Way Design Strategies 153 15.4 Operations Management Strategies 154 15.5 Sound Absorptive Treatments 155 15.6 Strategies Implemented by Receptors or Local Governments 157 Chapter 16 Strategy Effectiveness Flowcharts 158 16.1 Strategy Effectiveness Flowcharts Overview

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The most common approach that state departments of transportation (DOTs) use to address highway traffic noise impacts is noise barriers—usually noise walls.

The TRB National Cooperative Highway Research Program's NCHRP Research Report 984: Breaking Barriers: Alternative Approaches to Avoiding and Reducing Highway Traffic Noise Impacts presents the results of a review of innovative strategies to avoid and/or reduce highway noise impacts. A practitioner's handbook to identify which of these innovative strategies may be appropriate for a highway project is also included.

Supplemental to the report are Appendices A through E, covering terminology, a summary of 14 noise-reducing strategies, and further investigations of low berms, solid safety barriers, and acoustically soft ground; strategy flowcharts; and a final presentation.

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