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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. RÉ
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
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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
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areas of research needs to be included in the program are proposed of the researchers who performed the research and are not necessarily those
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The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished schol-
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and to their use for the general welfare. On the authority of the charter granted to it by the Congress in
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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. Ré 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.
