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NATIONAL NCHRP REPORT 635 COOPERATIVE HIGHWAY RESEARCH PROGRAM Acoustic Beamforming: Mapping Sources of Truck Noise

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TRANSPORTATION RESEARCH BOARD 2009 EXECUTIVE COMMITTEE* OFFICERS CHAIR: Adib K. Kanafani, Cahill Professor of Civil Engineering, University of California, Berkeley VICE CHAIR: Michael R. Morris, Director of Transportation, North Central Texas Council of Governments, Arlington EXECUTIVE DIRECTOR: Robert E. Skinner, Jr., Transportation Research Board MEMBERS J. Barry Barker, Executive Director, Transit Authority of River City, Louisville, KY Allen D. Biehler, Secretary, Pennsylvania DOT, Harrisburg Larry L. Brown, Sr., Executive Director, Mississippi DOT, Jackson Deborah H. Butler, Executive Vice President, Planning, and CIO, Norfolk Southern Corporation, Norfolk, VA William A.V. Clark, Professor, Department of Geography, University of California, Los Angeles David S. Ekern, Commissioner, Virginia DOT, Richmond Nicholas J. Garber, Henry L. Kinnier Professor, Department of Civil Engineering, University of Virginia, Charlottesville Jeffrey W. Hamiel, Executive Director, Metropolitan Airports Commission, Minneapolis, MN Edward A. (Ned) Helme, President, Center for Clean Air Policy, Washington, DC Will Kempton, Director, California DOT, Sacramento Susan Martinovich, Director, Nevada DOT, Carson City Debra L. Miller, Secretary, Kansas DOT, Topeka Neil J. Pedersen, Administrator, Maryland State Highway Administration, Baltimore Pete K. Rahn, Director, Missouri DOT, Jefferson City Sandra Rosenbloom, Professor of Planning, University of Arizona, Tucson Tracy L. Rosser, Vice President, Regional General Manager, Wal-Mart Stores, Inc., Mandeville, LA Rosa Clausell Rountree, CEOGeneral Manager, Transroute International Canada Services, Inc., Pitt Meadows, BC Steven T. Scalzo, Chief Operating Officer, Marine Resources Group, Seattle, WA Henry G. (Gerry) Schwartz, Jr., Chairman (retired), Jacobs/Sverdrup Civil, Inc., St. Louis, MO C. Michael Walton, Ernest H. Cockrell Centennial Chair in Engineering, University of Texas, Austin Linda S. Watson, CEO, LYNXCentral Florida Regional Transportation Authority, Orlando Steve Williams, Chairman and CEO, Maverick Transportation, Inc., Little Rock, AR EX OFFICIO MEMBERS Thad Allen (Adm., U.S. Coast Guard), Commandant, U.S. Coast Guard, Washington, DC Peter H. Appel, Administrator, Research and Innovative Technology Administration, U.S.DOT J. Randolph Babbitt, Administrator, Federal Aviation Administration, U.S.DOT Rebecca M. Brewster, President and COO, American Transportation Research Institute, Smyrna, GA George Bugliarello, President Emeritus and University Professor, Polytechnic Institute of New York University, Brooklyn; Foreign Secretary, National Academy of Engineering, Washington, DC James E. Caponiti, Acting Deputy Administrator, Maritime Administration, U.S.DOT Cynthia Douglass, Acting Deputy Administrator, Pipeline and Hazardous Materials Safety Administration, U.S.DOT LeRoy Gishi, Chief, Division of Transportation, Bureau of Indian Affairs, U.S. Department of the Interior, Washington, DC Edward R. Hamberger, President and CEO, Association of American Railroads, Washington, DC John C. Horsley, Executive Director, American Association of State Highway and Transportation Officials, Washington, DC Rose A. McMurry, Acting Deputy Administrator, Federal Motor Carrier Safety Administration, U.S.DOT Ronald Medford, Acting Deputy Administrator, National Highway Traffic Safety Administration, U.S.DOT William W. Millar, President, American Public Transportation Association, Washington, DC Jeffrey F. Paniati, Acting Deputy Administrator and Executive Director, Federal Highway Administration, U.S.DOT Peter Rogoff, Administrator, Federal Transit Administration, U.S.DOT Joseph C. Szabo, Administrator, Federal Railroad Administration, U.S.DOT Robert L. Van Antwerp (Lt. Gen., U.S. Army), Chief of Engineers and Commanding General, U.S. Army Corps of Engineers, Washington, DC *Membership as of June 2009.

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NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM NCHRP REPORT 635 Acoustic Beamforming: Mapping Sources of Truck Noise Yuriy A. Gurovich Kenneth J. Plotkin Daniel H. Robinson WYLE LABORATORIES INC. Arlington, VA William K. Blake Bethesda, MD Paul R. Donavan ILLINGWORTH & RODKIN, INC. Petaluma, CA Subject Areas Energy and Environment Highway and Facility Design Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration TRANSPORTATION RESEARCH BOARD WASHINGTON, D.C. 2009 www.TRB.org

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NATIONAL COOPERATIVE HIGHWAY NCHRP REPORT 635 RESEARCH PROGRAM Systematic, well-designed research provides the most effective Project 08-56 approach to the solution of many problems facing highway ISSN 0077-5614 administrators and engineers. Often, highway problems are of local ISBN 978-0-309-11800-2 interest and can best be studied by highway departments individually Library of Congress Control Number 2009935879 or in cooperation with their state universities and others. However, the 2009 Transportation Research Board accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of COPYRIGHT PERMISSION cooperative research. Authors herein are responsible for the authenticity of their materials and for obtaining In recognition of these needs, the highway administrators of the written permissions from publishers or persons who own the copyright to any previously American Association of State Highway and Transportation Officials published or copyrighted material used herein. initiated in 1962 an objective national highway research program Cooperative Research Programs (CRP) grants permission to reproduce material in this employing modern scientific techniques. This program is supported on 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, a continuing basis by funds from participating member states of the FMCSA, FTA, or Transit Development Corporation endorsement of a particular product, Association and it receives the full cooperation and support of the method, or practice. It is expected that those reproducing the material in this document for Federal Highway Administration, United States Department of 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 Transportation. from CRP. The Transportation Research Board of the National Academies was requested by the Association to administer the research program because of the Board's recognized objectivity and understanding of NOTICE modern research practices. The Board is uniquely suited for this purpose as it maintains an extensive committee structure from which The project that is the subject of this report was a part of the National Cooperative Highway Research Program conducted by the Transportation Research Board with the approval of authorities on any highway transportation subject may be drawn; it the Governing Board of the National Research Council. Such approval reflects the possesses avenues of communications and cooperation with federal, Governing Board's judgment that the program concerned is of national importance and state and local governmental agencies, universities, and industry; its appropriate with respect to both the purposes and resources of the National Research Council. relationship to the National Research Council is an insurance of The members of the technical committee selected to monitor this project and to review this objectivity; it maintains a full-time research correlation staff of report were chosen for recognized scholarly competence and with due consideration for the specialists in highway transportation matters to bring the findings of balance of disciplines appropriate to the project. The opinions and conclusions expressed research directly to those who are in a position to use them. or implied are those of the research agency that performed the research, and, while they have been accepted as appropriate by the technical committee, they are not necessarily those of The program is developed on the basis of research needs identified the Transportation Research Board, the National Research Council, the American by chief administrators of the highway and transportation departments Association of State Highway and Transportation Officials, or the Federal Highway and by committees of AASHTO. Each year, specific areas of research Administration, U.S. Department of Transportation. needs to be included in the program are proposed to the National Each report is reviewed and accepted for publication by the technical committee according Research Council and the Board by the American Association of State to procedures established and monitored by the Transportation Research Board Executive Committee and the Governing Board of the National Research Council. Highway and Transportation Officials. Research projects to fulfill these needs are defined by the Board, and qualified research agencies are The Transportation Research Board of the National Academies, the National Research Council, the Federal Highway Administration, the American Association of State Highway selected from those that have submitted proposals. Administration and and Transportation Officials, and the individual states participating in the National surveillance of research contracts are the responsibilities of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade Research Council and the Transportation Research Board. or manufacturers' names appear herein solely because they are considered essential to the object of this report. The needs for highway research are many, and the National Cooperative Highway Research Program can make significant contributions to the solution of 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 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 at: http://www.national-academies.org/trb/bookstore Printed in the United States of America

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COOPERATIVE RESEARCH PROGRAMS CRP STAFF FOR NCHRP REPORT 635 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs Christopher J. Hedges, Senior Program Officer Eileen P. Delaney, Director of Publications Natalie Barnes, Editor Doug English, Editor NCHRP PROJECT 08-56 PANEL Field of Transportation Planning--Area of Forecasting Kenneth D. Polcak, Maryland State Highway Administration, Baltimore, MD (Chair) Bruce C. Rymer, California DOT, Sacramento, CA Mariano Berrios, Florida DOT, Tallahassee, FL Robert M. Clarke, R.M. Clarke Counsulting, Caswell Beach, NC Deborah Freund, Federal Motor Carrier Safety Administration, Washington, DC Thomas A. Koos, Kentucky Transportation Cabinet, Frankfort, KY Larry J. Magnoni, Washington State DOT, Seattle, WA Judith L. Rochat, Research and Innovative Technology Administration, Cambridge, MA Michael A. Tunnell, American Transportation Research Institute, W. Sacramento, CA Mark A. Ferroni, FHWA Liaison Kimberly Fisher, TRB Liaison AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 08-56 by Wyle Laboratories, Inc., in Arlington, Virginia. Wyle Laboratories is the contractor for this study, with Dr. William Blake as the team consultant, and Illingworth & Rodkin, Inc. as the subcontractor. Proof-of-concept tests were performed at the International Truck and Engine Corporation's Truck Development and Technology Center in Ft. Wayne, Indiana. Dr. Kenneth Plotkin, Chief Scientist of Wyle Laboratories, was the Principal Investigator. The other authors of this report are Dr. Yuriy Gurovich, Acoustic Engineering Manager, and Daniel Robinson, Acoustical Engineer, of Wyle Laboratories; Dr. William Blake; and Dr. Paul Donavan of Illingworth & Rodkin. The authors are grateful to Mr. Les A. Grundman, Mr. Lee E. Schroeder, Mr. Chukwunonso Okoli and other International Truck employees for their invaluable active support during the proof-of-concept test- ing in Ft. Wayne. The authors also acknowledge Mr. Kenneth Polcak of the Maryland State Highway Administration for his assistance in conducting roadside truck noise measurements on US 301.

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FOREWORD By Christopher J. Hedges Staff Officer Transportation Research Board This report documents the use of the acoustic beamforming technique to pinpoint and measure noise levels from heavy truck traffic. The system uses an elliptical array of more than 70 microphones and data acquisition software to measure noise levels from a variety of noise sources on large trucks--including the engine, tires, mufflers, and exhaust pipes. The results validate the feasibility of beamforming technology, offer new insight into the distribution of truck noise sources, and provide valuable input to the design and testing of quieter pavements and noise barrier systems. This report will be of interest to anyone con- cerned with understanding and mitigating highway noise levels. Heavy trucks are significant contributors to overall traffic noise levels, and transporta- tion agencies need to better understand the location and relative levels of the principal noise sources (e.g., exhaust, mechanical, tirepavement, and aerodynamic) on heavy vehicles in order to more successfully mitigate traffic noise impacts. Typical measures used to mitigate highway traffic noise include noise barriers, land use planning, and insulation of structures. Some transportation agencies are investigating additional measures, such as quiet pavements. Newer acoustical measurement and map- ping techniques such as beamforming show promise for isolating the location and extent of the primary noise sources emanating from heavy trucks. Under NCHRP Project 08-56, a research team led by Wyle Laboratories designed and fabricated an elliptical beamform- ing array and tested a proof-of-concept design on stationary and moving trucks in a con- trolled setting. The tests were validated using known sound sources such as loudspeakers mounted on the vehicles. The resulting data were analyzed in the laboratory, and the tests validated the array's ability to localize and evaluate individual noise sources from the test vehicles. Following the proof-of-concept testing, the beamforming technique was used to measure truck noise sources under actual operating conditions on US 301 in Maryland. A total of 59 heavy truck and 4 medium truck pass-bys were measured, analyzed, and inter- preted. The results showed acoustic beamforming to be a very appropriate method for truck noise measurement and enabled the research team to optimize the microphone array and software for this purpose. The system was effective in isolating and measuring noise sources for both stationary and moving trucks with frequencies between 250 and 2000 Hz. The report includes a number of recommendations, including the updating of current traf- fic noise models, development of a national database for traffic noise models on different pavement types, and the further application of the study results to evaluate pavement and noise barrier designs.

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CONTENTS 1 Summary 6 Chapter 1 Background 6 1.1 Introduction 6 1.2 Heavy Truck Noise Sources 7 1.3 Source Identification Methods 9 1.4 Objective and Scope of Research 10 Chapter 2 Research Approach 10 Task 1. Analyze Literature, Research, and Current Practice 10 Task 2. Develop Experimental Design 10 Task 3. Perform Proof-of-Concept Test 10 Task 4. Submit Interim Report 10 Task 5. Execute Testing Plan 11 Task 6. Document and Analyze Results 11 Task 7. Summarize Key Findings 11 Task 8. Identify Future Research and Testing Needs 11 Task 9. Submit Final Report 12 Chapter 3 Research Findings 12 3.1 Review of Beamforming for Vehicle Noise Source Identification 12 3.2 Development of Experimental Design 12 3.2.1 Noise Mapping Technique Development 13 3.2.2 Microphone Array Design 14 3.2.3 Balance between Array Aperture and Spherical Spreading Loss 17 3.2.4 Design Conclusions 19 3.3 Experimental Microphone Array Engineering 19 3.3.1 Mechanical Design 19 3.3.2 Data Acquisition System 19 3.3.3 Preliminary Testing 20 3.4 Proof-of-Concept Testing 20 3.4.1 Low-Speed Tests 22 3.4.2 High-Speed Tests 23 3.4.3 Passby and Intensity Measurements 31 3.5 Proof-of-Concept Test Results 31 3.5.1 Beamformer Calibrations with Spherical Source 34 3.5.2 Benchmark Measurements of Spherical Source on Moving Truck with Competing Truck Noise 35 3.5.3 Benchmark Parallel Array-Based and Acoustic Intensity Measurements for Stationary Trucks

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41 3.5.4 Example Results from Low- and High-Speed Track Passbys 41 3.5.4.1 Analysis Technique for Low- and High-Speed Track Passbys 44 3.5.4.2 Passby Evaluations of the 5900i Truck: Localization of Engine Compartment and Tire Noise 46 3.5.4.3 Passby Evaluations of the 9200i Truck: Localization of Engine Compartment and Exhaust Noise 48 3.5.4.4 Evaluations of the Truck Acoustic Source Level During Passby as a Function of Vertical Elevation 53 3.6 Roadside Testing 53 3.6.1 Microphone Array Modifications 53 3.6.2 Data Post-Processing Algorithm Modifications 54 3.6.3 Test Site Selection 54 3.6.4 Roadside Measurement Setup 55 3.7 Results of Roadside Measurements 55 3.7.1 Calibration of the Test Site Geometry 55 3.7.2 Image Results of the Vehicle Passbys 68 3.7.3 Example Model of Truck Sources for Simulating Noise Propagation Results of the Vehicle Passbys 71 Chapter 4 Conclusions and Recommendations 71 4.1 Conclusions 71 4.2 Recommendations 73 References 75 Appendix A Array Microphone Coordinates 76 Appendix B Vertical Distributions of Noise Sources for Heavy Trucks 78 Appendix C Glossary of Special Terms