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2018 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 886 Field Evaluation of Reflected Noise from a Single Noise Barrier William Bowlby Rennie Williamson Darlene Reiter Clay Patton BowlBy & AssociAtes, inc. Franklin, TN Kenneth Kaliski Karl Washburn RsG White River Junction, VT Judy Rochat Jack Meighan Keith Yoerg Ats consultinG Pasadena, CA Ahmed El-Aassar Harvey Knauer GAnnett FleminG, inc. - enviRonmentAl Acoustics Fairfax, VA Gonzalo Sanchez Douglas Barrett sAnchez industRiAl desiGn, inc. Middleton, WI Subscriber Categories Design • Environment 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 research is the most effective way to solve many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation results in increasingly complex problems of wide inter- est to highway 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, United States Department of Transportation. 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 identified by chief administrators and other staff of the highway and transportation departments, by committees of AASHTO, and by the Federal Highway Administration. 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 http://www.national-academies.org and then searching for TRB Printed in the United States of America NCHRP RESEARCH REPORT 886 Project 25-44 ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-39067-5 Library of Congress Control Number 2018956753 © 2018 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, FMCSA, FRA, FTA, Office of the Assistant Secretary for Research and Technology, PHMSA, 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 image: Data collection site, I-270 in Ohio. 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; 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 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. C. D. Mote, Jr., 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.national-academies.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 increase the benefits that transportation contributes to society by providing leadership in transportation innovation and progress through research and information exchange, conducted within a setting that is objective, interdisciplinary, and multimodal. The Board’s varied committees, task forces, and panels annually engage about 7,000 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 CRP STAFF FOR NCHRP RESEARCH REPORT 886 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Ann M. Hartell, Senior Program Officer Gary A. Jenkins, Senior Program Assistant Eileen P. Delaney, Director of Publications Natalie Barnes, Associate Director of Publications Sharon Lamberton, Editor NCHRP PROJECT 25-44 PANEL Area Twenty-Five: Transportation Planning—Impact Analysis Kenneth D. Polcak, Maryland State Highway Administration, Baltimore, MD (Chair) David Masson Buehler, ICF International, Sacramento, CA James N. Grube, Hennepin County, Medina, MN Paul M. Kohler, CH2M, Richmond, VA Shuo Li, Indiana DOT, West Lafayette, IN Timothy V. Sexton, Minnesota DOT, St. Paul, MN Raphael E. “Ray” Umscheid, Texas DOT, Austin, TX George C. Wang, East Carolina University, Greenville, NC Cecilia Ho, FHWA Liaison Christine Gerencher, TRB Liaison AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 25-44 (Phases 1 and 2) by RSG with Bowlby & Associates, Inc. (B&A), ATS Consulting, Environmental Acoustics (EA, a Business Unit of Gannett Fleming, Inc.), and Sanchez Industrial Design, Inc. (SID). William Bowlby of B&A served as the technical lead for the project, and Kenneth Kaliski of RSG served as overall project manager. The lead authors of this report are Dr. Bowlby of B&A, Mr. Kaliski of RSG, Dr. Judy Rochat of ATS Consulting, Karl Washburn of RSG (now with Johnson Controls), and Rennie Williamson of B&A. Douglas Barrett of SID (now with Cross-Spectrum Acoustics, Inc.) was the lead author of the litera- ture review in Appendix A. The psychoacoustics section of Appendix E (available online) was written by Mr. Washburn and David-Michael Lozupone (now with Bose) of RSG. Dr. Rochat and Keith Yoerg of ATS had the lead on the Barrier Reflections Screening Tool user instructions in Appendix D, and Mr. Kaliski had the lead on the layperson’s guide (pamphlet). Darlene Reiter of B&A and Dr. Bowlby were the lead researchers on the study location selection criteria, recommended study locations, and data collection, processing, and analysis protocols. The Phase 1 noise measurements were conducted by different teams at each location, with Clay Patton of B&A at four of the sites and Gonzalo Sanchez of SID at three of them. Mr. Sanchez also provided the sound level and meteorological measurement systems and equipment technical support. Other field team members included Dr. Bowlby, Geoffrey Pratt, and Mr. Williamson of B&A; Dr. El-Aassar, Adam Alexander, Sonnie Peterson, Anjoli Martin, and John MacDonald of EA; Mr. Barrett, Paul Schick, Ryan (continued on page ix)

F O R E W O R D The research documented in this report analyzes the characteristics of sound reflected from a noise barrier to the opposite side of a highway. The study compared reflected noise from sound-reflecting barriers and from barriers with a sound-absorptive surface, examin- ing both the levels and frequencies of reflected noise to better understand how reflected noise is experienced by communities. The report will be of interest to noise specialists at state departments of transportation who are responsible for assessing anticipated noise effects of highway projects. Others who must understand and explain noise effects, including public involvement specialists, community impact assessment practitioners, and highway project managers, will also find relevant information in the report and accompanying materials. State departments of transportation (DOTs) periodically receive complaints from resi- dents about increases in traffic noise that residents believe are the result of noise reflected from a new noise barrier added across the roadway from them. Currently available analyti- cal tools are limited in their ability to evaluate reflected noise and some of the subtle changes in the quality of sound that can occur when it is reflected. Therefore, it is a challenge for DOTs to determine conclusively if complaints about reflected noise are the result of actual or perceived changes in noise characteristics, and to identify locations where absorptive surface treatments could be beneficial. As a result, where reflected noise may affect adjacent residents, many state DOTs take no action and a few address these concerns by specify- ing sound-absorbing surface treatments on all noise barriers. However, taking no action does not alleviate concerns and the routine installation of absorptive barrier surfaces may increase project construction costs as well as maintenance costs. The results of this study provide insights into the nature of reflected noise and can be used to support the appropri- ate use of sound-absorptive surfaces on barriers. The work was carried out by a consultant team led by Resource Systems Group (RSG) of White River Junction, Vermont, along with Bowlby & Associates, ATS Consulting, Environmental Acoustics/Gannett Fleming, and Sanchez Industrial Design. The research effort included collecting field data at eight monitoring sites, five with sound-reflective barriers and three with sound-absorptive barriers. Spectrograms, difference spectrograms, psychoacoustic metrics, and changes in sound levels were used to analyze differences in sound levels and frequency patterns associated with the two types of noise barriers. In addition to the report, the research team produced a series of appendices detailing the data collection protocol, analysis methods, and results. A review of literature on community noise issues that have led to previous investigations of noise reflected from barriers is also provided. To support the application of the results to practice, a simple, spreadsheet-based By Ann M. Hartell Staff Officer Transportation Research Board

tool was developed to help noise analysts estimate the effects of reflected noise for projects. Also accompanying the report is a pamphlet designed to communicate the main concepts from the research to nontechnical audiences. The pamphlet can be customized by a DOT for use in connection with a specific, project-related outreach effort or for more generalized distribution. These materials are available for viewing or download from www.trb.org by searching for “NCHRP Research Report 886.”

C O N T E N T S 1 Summary 7 Chapter 1 Introduction 7 The Problem 8 Project Objectives and Approach 10 Chapter 2 Research Approach 10 Research Tasks 10 Protocol for Data Collection and Analysis 13 FHWA Method Data Processing 14 FHWA Method Data Analysis Protocol 14 Spectrogram Data Processing and Analysis Protocol 15 Psychoacoustics Processing and Analysis Protocol 17 Chapter 3 Sound-Reflecting Barrier Study Locations 17 Study Location Selection Criteria and Process 17 Selected Locations 19 I-24, Murfreesboro, Tennessee (Location BA-1, Sound-Reflecting Barrier) 21 SR-155 (Briley Parkway), Nashville, Tennessee (Location BA-3, Sound-Reflecting Barrier) 26 I-90, Rockford, Illinois (Location SID-1, Sound-Reflecting Barrier) 27 SR-71, Chino Hills, California (Location ATS-3, Sound-Reflecting Barrier) 28 MD-5, Hughesville, Maryland (Location EA-5, Sound-Reflecting Barrier) 28 Summary of Microphone Positions for Sound-Reflecting Barriers 40 Chapter 4 Sound-Absorbing Barrier Study Locations 40 Selected Locations 40 I-75, Troy, Ohio (Location OH-1, Sound-Absorbing Barrier) 42 I-70, South Vienna, Ohio (Location OH-2, Sound-Absorbing Barrier) 43 I-270, Grove City, Ohio (Location OH-3, Sound-Absorbing Barrier) 53 Chapter 5 Findings: Sound-Reflecting Barriers 53 Sound-Reflecting Barrier Finding 1: Measured Broadband Equivalent Sound Levels 56 Sound-Reflecting Barrier Finding 2: Frequency-Specific Differences in Barrier and No-Barrier Levels 56 Sound-Reflecting Barrier Finding 3: Effects Between the Barrier and the Road 61 Sound-Reflecting Barrier Finding 4: Background Levels Between the Barrier and the Road 64 Sound-Reflecting Barrier Finding 5: Reference Microphone Position Atop the Barrier 66 Sound-Reflecting Barrier Finding 6: Effects at Lower Microphones Near the Roadway Edge

66 Sound-Reflecting Barrier Finding 7: Background Levels Near the Edge of the Road for the Lower-Height Microphones 68 Sound-Reflecting Barrier Finding 8: Effects Farther Back from the Road, but Still Within 100 ft. 73 Sound-Reflecting Barrier Finding 9: Background Levels Farther Back from the Road but Still Within 100 ft. 75 Sound-Reflecting Barrier Finding 10: Increase in Broadband and Spectral Levels at 400 ft. from the Road 76 Sound-Reflecting Barrier Finding 11: Ln Descriptors at 400 ft. from the Road 78 Sound-Reflecting Barrier Finding 12: Higher Microphone Compared to Lower Microphone 79 Sound-Reflecting Barrier Finding 13: No Effect of Traffic Volume 80 Sound-Reflecting Barrier Finding 14: Effects of Meteorological Classes 82 Sound-Reflecting Barrier Finding 15: Spectrograms Show Increased and Sustained Sound Levels 88 Sound-Reflecting Barrier Finding 16: Psychoacoustic Metrics of UBA, PA, and CSA 92 Sound-Reflecting Barrier Finding 17: Annoyance Metrics 93 Sound-Reflecting Barrier Finding 18: Annoyance Metrics as a Function of Traffic Volume 95 Chapter 6 Findings: Sound-Absorbing Barriers Compared to Sound-Reflecting Barriers 95 Comparison Finding 1: Differences in Broadband Levels at the Reference Microphones 97 Comparison Finding 2: Differences in Broadband Levels Opposite the Barrier at Different Microphone Heights 99 Comparison Finding 3: Differences in Broadband Levels Opposite the Barrier at Different Microphone Distances 101 Comparison Finding 4: One-Third Octave Band Differences at Different Microphone Heights 106 Comparison Finding 5: One-Third Octave Band Differences at Different Microphone Distances 110 Comparison Finding 6: Broadband L90 and L99 Statistical Descriptors 114 Comparison Finding 7: Broadband L90 and L99 Statistical Descriptors at Different Distances Across from the I-75 Sound-Absorbing Barrier 118 Comparison Finding 8: One-Third Octave Band L90 and L99 Descriptors 124 Comparison Finding 9: Effects of Site Differences 127 Comparison Finding 10: Spectrograms Indicate that Sound-Absorbing Barrier Effects Are Subtle 130 Comparison Finding 11: Difference Spectrograms Indicate that Barrier Reflections Result in Comb Filtering, Which Changes the Sound Quality 136 Comparison Finding 12: The Barrier Reflections Screening Tool Can Be Used to Estimate Barrier Reflection Effects

139 Chapter 7 Applications, Conclusions, Recommendations, and Suggested Research 139 Applications 140 Conclusions 141 Recommendations 142 Suggested Research 145 References A-1 Appendix A Literature Review B-1 Appendix B Phase 2 (Sound-Absorbing Barriers)— Detailed Analysis and Results C-1 Appendix C Comparison of Phase 1 and Phase 2 Results D-1 Appendix D Using the Barrier Reflections Screening Tool xi Content Available Online Cranfill, and Lisa Sanchez of SID; and Dr. Rochat, Shannon McKenna, and Tony Evans of ATS Consult- ing. Phase 1 data reduction, processing, analysis, and quality control were performed by Mr. Sanchez and Mr. Schick of SID; Dr. Bowlby, Mr. Williamson, Mr. Pratt, and Mr. Patton of B&A; Dr. Rochat, Hugh Saurenman, Chris Ono, Jack Meighan, and Jackie Chavez of ATS; Mr. Kaliski, Mr. Washburn, and Isaac Old of RSG; and Dr. El-Aassar, Harvey Knauer, Mr. Alexander, Ms. Peterson, Ms. Martin, and Dr. MacDonald of EA. The noise measurements in Phase 2 were performed by Mr. Patton, Ms. Martin, Mr. Meighan, and Ryan Haac of RSG, who also provided technical support for the sound level and meteorological measure- ment systems provided by RSG. Phase 2 data reduction, processing, analysis, and quality control were performed by Dr. Bowlby, Mr. Williamson, and Mr. Patton of B&A; Dr. Rochat, Mr. Meighan, Shawn Duenas and Mr. Yoerg of ATS; and Mr. Kaliski and Mr. Haac of RSG. The research team acknowledges the valuable input and direction from the project’s technical advisory panel. AUTHOR ACKNOWLEDGMENTS (Continued )

1 S U M M A R Y Through field measurements and audio recordings, this research studied the pos- sible changes in sound levels and sound characteristics caused by sound reflections off a noise barrier on the opposite side of a highway. Phase 1 examined sound-reflecting barriers, while Phase 2 focused on sound-absorbing barriers. A simplified screening tool for estimating sound level increases opposite a barrier was developed, as was a pamphlet, titled “Reflected Sound from Highway Noise Barriers,” presenting a layperson’s guide to understanding sound reflections off highway noise barriers. The analysis was done using: • A modification to a method in a FHWA noise measurement manual in which simul- taneous measurements were made at a “Barrier” site and at an equivalent, adjacent “No-Barrier” site under equivalent source and meteorological conditions (FHWA Method); • Acoustical spectrograms, which show the frequency content of sound as a function of time; • Psychoacoustic measures of loudness, sharpness, roughness, and fluctuation strength combined into metrics of annoyance (Phase 1 only); and • Difference spectrograms, which show subtle differences between two spectrograms, and comb-filtering analysis, which examines the relationship of peak frequencies in the dif- ference spectrograms (Phase 2 only). Changes in statistical exceedance (Ln) descriptors also were addressed. Broadband unweighted sound pressure levels (dBZ) and A-weighted sound levels (dBA) were studied, as well as one-third octave band sound pressure levels. In this report, the unit dB is generally used when referring to changes in level for both unweighted and A-weighted sound level measurements. Locations For Phase 1, five reflective barrier locations were selected for data collection and analysis: • I-24, Murfreesboro, Tennessee (labeled BA-1); • SR-155 (Briley Parkway), Nashville, Tennessee (labeled BA-3); • I-90, Rockford, Illinois (labeled SID-1); • SR-71, Chino Hills, California (labeled ATS-3); and • MD-5, Hughesville, Maryland (labeled EA-5). For Phase 2, three absorptive barrier locations were selected for data collection and analysis: • I-75, Troy, Ohio (labeled OH-1); • I-70, South Vienna, Ohio (labeled OH-2); and • I-270, Grove City, Ohio (labeled OH-3). Field Evaluation of Reflected Noise from a Single Noise Barrier

2 Data Collection and Analysis With two exceptions—SR-155 (Briley Parkway) and I-270—six sound level analyzers were deployed at each location: three at the Barrier site and three at the adjacent No-Barrier site. Each site had a reference microphone on the Barrier side of the road and two pairs of “community” microphones on the opposite side of the road from the barrier. These micro- phones were positioned in terms of their distance from the road and height above the road such that the results from each pair were directly comparable. The I-24 and SR-71 sound- reflecting locations also afforded the opportunity to place the Barrier reference microphone between the barrier and the road so that it could be compared to the No-Barrier reference microphone as a primary point that might be affected by reflected noise. Evening measure- ments were made at the Briley Parkway and MD-5 sound-reflecting locations and the I-270 location. These measurements were made to capture isolated, single-vehicle pass-by events. A meteorological station collected simultaneous wind speed and direction, and a video camera and laser speed gun were used to collect traffic volume and classification data and travel speeds. Four hours of data were collected at each location, logged at 1-second intervals, and pro- cessed in 1-minute periods. The 1-minute data blocks were examined to see if there was contamination from intrusive noise sources, and contaminated blocks were eliminated as necessary. The remaining data blocks were then grouped into 5-minute periods for com- parability. For highway traffic, this amount of time averages the short-term vehicle pass-by and intervening lulls and allows the same vehicles to be captured at Barrier and No-Barrier microphones, with only slight differences at the beginning and ending of the block. Broadband A-weighted sound levels (dBA) and unweighted sound pressure levels (dBZ) were examined for the 5-minute periods without consideration of the source and meteo- rological equivalence of the periods to each other. This analysis reveals evidence of sound level increases at the Barrier microphones, including both the reference microphones posi- tioned in front of the barrier and the community microphones positioned across the road. The data blocks for the 5-minute periods were then tested for source equivalence—in terms of the reference sound level data and speed data—and for meteorological equivalence. The meteorological classes consisted of a combination of wind direction (Upwind, Calm, and Downwind) and temperature gradient (Lapse, Neutral, and Inversion). When three or more equivalent 5-minute periods were identified based on source and meteorological class, the data blocks were grouped together and their broadband and one-third octave band sound level differences were examined in terms of the 5-minute equivalent sound pressure level, represented as Leq (5 min.). The 1-second data also were processed to determine statistical exceedance descrip- tors (Ln, ranging from L1 to L99) for both the broadband levels and the one-third octave band levels. Phase 1: Findings, Sound-Reflecting Barriers From the above data, the following findings were developed regarding the Phase 1 (sound-reflecting) barriers: • Measured broadband unweighted sound pressure levels are generally higher at the Barrier microphones (Barrier levels) than at the No-Barrier microphones (No-Barrier levels). Likewise, measured A-weighted sound levels are generally higher at the Barrier micro- phones than at the No-Barrier microphones. • The differences in Barrier and No-Barrier levels are frequency specific and vary by loca- tion and site. Clear examples exist of enhanced levels opposite several of the barriers compared to the corresponding No-Barrier positions.

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TRB's National Cooperative Highway Research Program (NCHRP) Research Report 886: Field Evaluation of Reflected Noise from a Single Noise Barrier analyzes the characteristics of sound reflected from a noise barrier to the opposite side of a highway. State departments of transportation (DOTs) periodically receive complaints from residents about increases in traffic noise that residents believe are the result of noise reflected from a new noise barrier added across the roadway from them. Currently available analytical tools are limited in their ability to evaluate reflected noise and some of the subtle changes in the quality of sound that can occur when it is reflected. Therefore, it is a challenge for DOTs to determine conclusively if complaints about reflected noise are the result of actual or perceived changes in noise characteristics, and to identify locations where absorptive surface treatments could be beneficial.

The study compares reflected noise from sound-reflecting barriers and from barriers with a sound-absorptive surface. It examines both the levels and frequencies of reflected noise to better understand how reflected noise is experienced by communities.

The full report, which includes four detailed appendices, is 27 MB and may take time to download. It is accompanied by several appendices, a tool, and a guide:

A presentation file that summarizes the research also is available on the report project page.

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