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NCHRP NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM SYNTHESIS 431 Practices to Manage Traffic Sign Retroreflectivity A Synthesis of Highway Practice

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TRANSPORTATION RESEARCH BOARD 2012 EXECUTIVE COMMITTEE* OFFICERS Chair: Sandra Rosenbloom, Professor of Planning, University of Arizona, Tucson Vice Chair: Deborah H. Butler, Executive Vice President, Planning, and CIO, Norfolk Southern Corporation, Norfolk, VA Executive Director: Robert E. Skinner, Jr., Transportation Research Board MEMBERS J. Barry Barker, Executive Director, Transit Authority of River City, Louisville, KY William A.V. Clark, Professor of Geography and Professor of Statistics, Department of Geography, University of California, Los Angeles Eugene A. Conti, Jr., Secretary of Transportation, North Carolina DOT, Raleigh James M. Crites, Executive Vice President of Operations, Dallas-Fort Worth International Airport, TX Paula J. C. Hammond, Secretary, Washington State DOT, Olympia Michael W. Hancock, Secretary, Kentucky Transportation Cabinet, Frankfort Chris T. Hendrickson, Duquesne Light Professor of Engineering, Carnegie-Mellon University, Pittsburgh, PA Adib K. Kanafani, Professor of the Graduate School, University of California, Berkeley Gary P. LaGrange, President and CEO, Port of New Orleans, LA Michael P. Lewis, Director, Rhode Island DOT, Providence Susan Martinovich, Director, Nevada DOT, Carson City Joan McDonald, Commissioner, New York State DOT, Albany Michael R. Morris, Director of Transportation, North Central Texas Council of Governments, Arlington Neil J. Pedersen, Consultant, Silver Spring, MD Tracy L. Rosser, Vice President, Regional General Manager, Wal-Mart Stores, Inc., Mandeville, LA Henry G. (Gerry) Schwartz, Jr., Chairman (retired), Jacobs/Sverdrup Civil, Inc., St. Louis, MO Beverly A. Scott, General Manager and CEO, Metropolitan Atlanta Rapid Transit Authority, Atlanta, GA David Seltzer, Principal, Mercator Advisors LLC, Philadelphia, PA Kumares C. Sinha, Olson Distinguished Professor of Civil Engineering, Purdue University, West Lafayette, IN Thomas K. Sorel, Commissioner, Minnesota DOT, St. Paul Daniel Sperling, Professor of Civil Engineering and Environmental Science and Policy; Director, Institute of Transportation Studies; and Acting Director, Energy Efficiency Center, University of California, Davis Kirk T. Steudle, Director, Michigan DOT, Lansing Douglas W. Stotlar, President and CEO, Con-Way, Inc., Ann Arbor, MI C. Michael Walton, Ernest H. Cockrell Centennial Chair in Engineering, University of Texas, Austin ex officio members Rebecca M. Brewster, President and COO, American Transportation Research Institute, Smyrna, GA Anne S. Ferro, Administrator, Federal Motor Carrier Safety Administration, U.S.DOT LeRoy Gishi, Chief, Division of Transportation, Bureau of Indian Affairs, U.S. Department of the Interior, Washington, DC John T. Gray II, Senior Vice President, Policy and Economics, Association of American Railroads, Washington, DC John C. Horsley, Executive Director, American Association of State Highway and Transportation Officials, Washington, DC Michael P. Huerta, Acting Administrator, Federal Aviation Administration, U.S.DOT David T. Matsuda, Administrator, Maritime Administration, U.S.DOT Michael P. Melaniphy, President and CEO, American Public Transportation Association, Washington, DC Victor M. Mendez, Administrator, Federal Highway Administration, U.S.DOT Tara O'Toole, Under Secretary for Science and Technology, U.S. Department of Homeland Security, Washington, DC Robert J. Papp (Adm., U.S. Coast Guard), Commandant, U.S. Coast Guard, U.S. Department of Homeland Security, Washington, DC Cynthia L. Quarterman, Administrator, Pipeline and Hazardous Materials Safety Administration, U.S.DOT Peter M. Rogoff, Administrator, Federal Transit Administration, U.S.DOT David L. Strickland, Administrator, National Highway Traffic Safety Administration, U.S.DOT Joseph C. Szabo, Administrator, Federal Railroad Administration, U.S.DOT Polly Trottenberg, Assistant Secretary for Transportation Policy, 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 Barry R. Wallerstein, Executive Officer, South Coast Air Quality Management District, Diamond Bar, CA Gregory D. Winfree, Acting Administrator, Research and Innovative Technology Administration, U.S.DOT *Membership as of February 2012.

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N AT I O N A L C O O P E R AT I V E H I G H WAY R E S E A R C H P R O G R A M NCHRP SYNTHESIS 431 Practices to Manage Traffic Sign Retroreflectivity A Synthesis of Highway Practice Consultants JONATHAN M. R and PAUL J. CARLSON Texas Transportation Institute S ubscriber C ategories Highways Maintenance and Preservation Operations and Traffic Management Public Transportation Safety and Human Factors 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. 2012 www.TRB.org

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NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM NCHRPSYNTHESIS 431 Systematic, well-designed research provides the most effective Project 20-05, Topic 42-12 approach to the solution of many problems facing highway ISSN 0547-5570 administrators and engineers. Often, highway problems are of local ISBN 978-0-309-22360-7 interest and can best be studied by highway departments Library of Congress Control No. 2012934384 individually or in cooperation with their state universities and 2012 National Academy of Sciences. All rights reserved. others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a COPYRIGHT INFORMATION coordinated program of cooperative research. Authors herein are responsible for the authenticity of their materials and for In recognition of these needs, the highway administrators of the obtaining written permissions from publishers or persons who own the American Association of State Highway and Transportation copyright to any previously published or copyrighted material used herein. Officials initiated in 1962 an objective national highway research Cooperative Research Programs (CRP) grants permission to reproduce program employing modern scientific techniques. This program is material in this publication for classroom and not-for-profit purposes. supported on a continuing basis by funds from participating Permission is given with the understanding that none of the material will member states of the Association and it receives the full cooperation be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FTA, or Transit and support of the Federal Highway Administration, United States Development Corporation endorsement of a particular product, method, or Department of Transportation. practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment The Transportation Research Board of the National Academies of the source of any reprinted or reproduced material. For other uses of the was requested by the Association to administer the research material, request permission from CRP. program because of the Board's recognized objectivity and understanding of modern research practices. The Board is uniquely suited for this purpose as it maintains an extensive committee structure from which authorities on any highway transportation NOTICE subject may be drawn; it possesses avenues of communications and The project that is the subject of this report was a part of the National cooperation with federal, state, and local governmental agencies, Cooperative Highway Research Program, conducted by the Transportation universities, and industry; its relationship to the National Research Research Board with the approval of the Governing Board of the National Council is an insurance of objectivity; it maintains a full-time Research Council. research correlation staff of specialists in highway transportation The members of the technical panel selected to monitor this project and matters to bring the findings of research directly to those who are in to review this report were chosen for their special competencies and with a position to use them. regard for appropriate balance. The report was reviewed by the technical panel and accepted for publication according to procedures established The program is developed on the basis of research needs and overseen by the Transportation Research Board and approved by the identified by chief administrators of the highway and transportation Governing Board of the National Research Council. departments and by committees of AASHTO. Each year, specific The opinions and conclusions expressed or implied in this report are those areas of research needs to be included in the program are proposed of the researchers who performed the research and are not necessarily those to the National Research Council and the Board by the American of the Transportation Research Board, the National Research Council, or the Association of State Highway and Transportation Officials. program sponsors. Research projects to fulfill these needs are defined by the Board, and qualified research agencies are selected from those that have submitted proposals. Administration and surveillance of research The Transportation Research Board of the National Academies, the National contracts are the responsibilities of the National Research Council Research Council, and the sponsors of the National Cooperative Highway and the Transportation Research Board. Research Program do not endorse products or manufacturers. Trade or The needs for highway research are many, and the National manufacturers' names appear herein solely because they are considered Cooperative Highway Research Program can make significant essential to the object of the report. 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 Note: The Transportation Research Board of the National Academies, the Washington, DC 20001 National Research Council, the Federal Highway Administration, the American Association of State Highway and Transportation Officials, and the individual and can be ordered through the Internet at: states participating in the National Cooperative Highway Research Program do http://www.national-academies.org/trb/bookstore not endorse products or manufacturers. Trade or manufacturers' names appear herein solely because they are considered essential to the object of this report. Printed in the United States of America

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The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished schol- ars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. On the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and techni- cal matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Acad- emy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achieve- ments of engineers. Dr. Charles M. Vest is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, on its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Acad- emy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. Charles M. Vest are chair and vice chair, respectively, of the National Research Council. The Transportation Research Board is one of six major divisions of the National Research Council. The mission of the Transportation Research Board is to provide leadership in transportation innovation and progress through research and information exchange, conducted within a setting that is objective, interdisci- plinary, and multimodal. The Board's varied activities 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 Transporta- tion, and other organizations and individuals interested in the development of transportation. www.TRB.org www.national-academies.org

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NCHRP COMMITTEE FOR PROJECT 20-05 COOPERATIVE RESEARCH PROGRAMS STAFF CHRISTOPHER W. JENKS, Director, Cooperative CHAIR Research Programs CATHERINE NELSON, Oregon DOT CRAWFORD F. JENCKS, Deputy Director, Cooperative Research Programs MEMBERS NANDA SRINIVASAN, Senior Program Officer KATHLEEN S. AMES, Michael Baker, Jr., Inc. EILEEN P. DELANEY, Director of Publications STUART D. ANDERSON, Texas A&M University BRIAN A. BLANCHARD, Florida DOT SYNTHESIS STUDIES STAFF CYNTHIA J. BURBANK, PB Americas, Inc. STEPHEN R. GODWIN, Director for Studies and Special Programs LISA FREESE, Scott County (MN) Community Services Division JON M. WILLIAMS, Program Director, IDEA and Synthesis Studies MALCOLM T. KERLEY, Virginia DOT JO ALLEN GAUSE, Senior Program Officer RICHARD D. LAND, California DOT GAIL R. STABA, Senior Program Officer JOHN M. MASON, JR., Auburn University DONNA L. VLASAK, Senior Program Officer ROGER OLSON, Minnesota DOT TANYA M. ZWAHLEN, Consultant ROBERT L. SACK, New York State DOT DON TIPPMAN, Senior Editor FRANCINE SHAW-WHITSON, Federal Highway Administration CHERYL KEITH, Senior Program Assistant LARRY VELASQUEZ, JAVEL Engineering, LLC DEMISHA WILLIAMS, Senior Program Assistant DEBBIE IRVIN, Program Associate FHWA LIAISON JACK JERNIGAN TOPIC PANEL MARY LYNN TISCHER PETER R. BRETT, Hillsborough County, Tampa, FL ED COURVILLE, Louisiana Department of Transportation and TRB LIAISON Development, Baton Rouge STEPHEN F. MAHER RONALD W. ECK, West Virginia University JAMES W. ELLISON, Federal Way, WA THOMAS HONICH, Missouri Department of Transportation FRANK N. LISLE, Transportation Research Board MATTHEW R. RAUCH, Bureau of Highway Operations, Madison, WI PAUL LEONARD STOUT, Maryland State Highway Administration, Hanover GEORGE MERRITT, Federal Highway Administration (Liaison) CATHERINE M. SATTERFIELD, Federal Highway Administration, Matteson, IL (Liaison) Cover figure: Research Associate Dan Walker collecting retro values of a typical stop sign. Photo by TTI staff Fan Ye.

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FOREWORD Highway administrators, engineers, and researchers often face problems for which infor- mation already exists, either in documented form or as undocumented experience and prac- tice. This information may be fragmented, scattered, and unevaluated. As a consequence, full knowledge of what has been learned about a problem may not be brought to bear on its solution. Costly research findings may go unused, valuable experience may be overlooked, and due consideration may not be given to recommended practices for solving or alleviat- ing the problem. There is information on nearly every subject of concern to highway administrators and engineers. Much of it derives from research or from the work of practitioners faced with problems in their day-to-day work. To provide a systematic means for assembling and evaluating such useful information and to make it available to the entire highway com- munity, the American Association of State Highway and Transportation Officials--through the mechanism of the National Cooperative Highway Research Program--authorized the Transportation Research Board to undertake a continuing study. This study, NCHRP Project 20-5, "Synthesis of Information Related to Highway Problems," searches out and syn- thesizes useful knowledge from all available sources and prepares concise, documented reports on specific topics. Reports from this endeavor constitute an NCHRP report series, Synthesis of Highway Practice. This synthesis series reports on current knowledge and practice, in a compact format, without the detailed directions usually found in handbooks or design manuals. Each report in the series provides a compendium of the best knowledge available on those measures found to be the most successful in resolving specific problems. PREFACE "Traffic sign retroreflectivity" is a sign property which, during nighttime, causes light By Jon M. Williams from a vehicle's headlamps to be reflected back to the driver, giving the sign an illumi- Program Director nated appearance. The federal government has established guidance to ensure that agencies Transportation responsible for traffic signs will bring their signs up to an acceptable standard of retroreflec- Research Board tivity. The objective of this study is to provide examples of effective practices that illustrate how different types of agencies can meet the retroreflectivity requirements. Information was gathered through a literature review and telephone surveys. Jonathan M. R and Paul J. Carlson of the Texas Transportation Institute collected and synthesized the information and wrote the report. The members of the topic panel are acknowledged on the preceding page. This synthesis is an immediately useful document that records the practices that were acceptable within the limitations of the knowledge available at the time of its preparation. As progress in research and practice continues, new knowledge will be added to that now at hand.

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CONTENTS 1Summary 3 Chapter OneIntroduction Background, 3 Synthesis Objective, 4 Study Approach, 4 6 Chapter Two Description Of Sign Retroreflectivity Maintenance Methods Sign Retroreflectivity Maintenance Methods, 6 Sign Service Life, 12 14 Chapter Three Range Of Practices Survey Results, 14 Visual Nighttime Inspection, 14 Measured Retroreflectivity, 16 Expected Sign Life, 17 Blanket Replacement, 18 Control Signs, 18 Sign Inventories, 19 22 Chapter Four Case Studies Clifton Park, New York, 22 St. Louis County, Minnesota, 23 Phoenix, Arizona, 24 Missouri Department of Transportation, 25 27 Chapter Five Effective Practices General Sign Practices, 27 Visual Nighttime Inspection, 27 Measured Retroreflectivity, 28 Expected Sign Life, 28 Blanket Replacement, 28 Control Signs, 28 29 Chapter SixResearch In Progress And Research Needs 30 Chapter SevenConclusions 31References 32 Appendix AMinimum Maintained Retroreflectivity Levels Resources

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38 Appendix B Telephone Survey 40 Appendix C Survey Participants 43 Appendix D Myths and Other Frequently Asked Questions Note: Many of the photographs, figures, and tables in this report have been converted from color to grayscale for printing. The electronic version of the report (posted on the Web at www.trb.org) retains the color versions.