Guidelines for Nighttime Visibility of Overhead Signs (2016)

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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 REPORT 828 Guidelines for Nighttime Visibility of Overhead Signs Paul J. Carlson Bradford K. Brimley Jeff Miles Susan Chrysler Texas a&M TransporTaTion insTiTuTe College Station, TX and Ronald B. Gibbons Travis Terry Virginia Tech TransporTaTion insTiTuTe Blacksburg, VA Subscriber Categories Operations and Traffic Management • Safety and Human Factors TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2016 www.TRB.org 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 Academies is an insurance of objectivity; and TRB maintains a full-time staff of specialists in high- way 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 transporta- tion departments and by committees of AASHTO. Topics of the highest merit are selected by the AASHTO Standing Committee on Research (SCOR), and each year SCOR’s recommendations are proposed to the AASHTO Board of Directors and the 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 Acad- emies 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 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 REPORT 828 Project 05-20 ISSN 0077-5614 ISBN 978-0-309-37547-4 Library of Congress Control Number 2016941498 © 2016 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. NOTICE The 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. Ralph J. Cicerone 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 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 AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 05-20 by the Texas A&M Transporta- tion Institute (TTI) and the Virginia Tech Transportation Institute (VTTI). TTI was the contractor for this study, with VTTI serving as a subcontractor. CRP STAFF FOR NCHRP REPORT 828 Christopher W. Jenks, Director, Cooperative Research Programs Christopher Hedges, Manager, National Cooperative Highway Research Program Edward T. Harrigan, Senior Program Officer Anthony P. Avery, Senior Program Assistant Eileen P. Delaney, Director of Publications Kami Cabral, Editor NCHRP PROJECT 05-20 PANEL Field of Traffic—Area of Illumination and Visibility Paul L. Stout, Maryland State Highway Administration, Hanover, MD (Chair) Tom A. Heydel, Wisconsin DOT, Waukesha, WI Rashad M. Hanbali, American University of Madaba, Cape Coral, FL Carlos Ibarra, City of Plano, Plano, TX Jonathan Upchurch, Consultant, Ivins, UT Ted Whitmore, West Virginia DOT, Charleston, WV Kevin Sylvester, FHWA Liaison Richard A. Cunard, TRB Liaison

F O R E W O R D This report presents proposed guidelines for nighttime overhead sign visibility, formatted as a potential replacement for the current Chapter 10, Roadway Sign Lighting, in the 2005 AASHTO Roadway Lighting Design Guide. The proposed Chapter 10 is called “Overhead Sign Lighting.” Thus, the report will be of immediate interest to engineers in state highway agencies and other transportation agencies with responsibility for the management of over- head guide signs and street signs. A frequent dilemma facing highway agencies is deciding how to provide effective nighttime performance for overhead signs. While the Manual on Uniform Traffic Control Devices (MUTCD) provides minimum retroreflectivity standards for overhead signs, there are few guidelines that agencies can reference to decide how to provide sufficient nighttime performance of overhead signs in site-specific situations. The common wisdom is that overhead guide sign lighting may be turned off in rural areas if highly reflective sheeting materials are used. However, there is little consensus about the use of lighting in suburban and urban areas where visual backgrounds and roadway geometries are more complex. Moreover, the presence and amount of roadway lighting, roadway geometry, traffic volume, traffic speed, and sign position and orientation with respect to oncoming traffic can also create challenges to the effective nighttime performance of overhead signs. The objective of this research was to develop guidelines for providing effective nighttime performance of overhead guide signs in site-specific situations. The research was conducted by the Texas A&M Transportation Institute, College Station, Texas, supported by the Virginia Tech Transportation Institute, Blacksburg, Virginia. The research was conducted in two phases. In the first phase, a closed-course study was conducted at the Virginia Smart Road at the Virginia Tech Transportation Institute. The goal of this study was to determine legibility distances for drivers in controlled conditions for three different sign legend and background configurations lit by either high pressure sodium or light emitting diode systems or they were unlit. In the second phase, an open-road study was conducted by the Texas A&M Transportation Institute in three urban areas—Bryan/ College Station, Texas; San Antonio, Texas; and Orlando, Florida. The goal of the open-road study was to determine the effects of sign luminance and visual complexity on the distance at which a driver can read overhead signs and street signs. Both studies employed cohorts of recruited drivers evenly split in terms of gender and age. The key outcome of the research is the proposed “Guidelines for Nighttime Overhead Sign Visibility” presented as a proposed replacement for the current Chapter 10, Roadway Sign Lighting, in the AASHTO Roadway Lighting Design Guide. The proposed Chapter 10 is called Overhead Sign Lighting and is included in this report in Appendix D. The closed-course study By Edward T. Harrigan Staff Officer Transportation Research Board

found that sign lighting does not significantly impact legibility distance of signs in rural and dark areas, suggesting that sufficient illumination for visibility was provided by headlamps. Using software developed for the open-road study, digital images were analyzed to quanti- tatively measure visual complexity in urban and suburban areas. Visual complexity of sign surroundings was found to reduce the distance at which a driver can correctly recognize information from signs, however, this effect can be countered by increases in the legend luminance. This report fully documents the research and includes four appendixes: Appendix A Incremental Effects of Light Sources and Sign Sheeting on Legend Luminance for Overhead Guide Signs Appendix B Assessment of Background Complexity Using Digital Images of Roadway Scenes by Image Processing Appendix C Open-Road Study Details Appendix D Guidelines for Nighttime Overhead Sign Visibility

C O N T E N T S 1 Summary 3 Chapter 1 Introduction 3 Research Objectives 3 Research Approach 5 Chapter 2 Background 5 Luminance Requirements for Sign Visibility 6 Lighting Sources 12 Roadway Lighting 13 Effects of Complex Environments on Sign Visibility 13 Measuring Sign Visual Performance: Recognition and Legibility 15 Conclusion 16 Chapter 3 Closed-Course Study 16 Experimental Design 23 Analyses 26 Conclusions 27 Chapter 4 Open-Road Study 27 Experimental Design 31 Analysis 33 Conclusions 35 Chapter 5 Research Findings 35 Key Findings 36 Conclusion 37 Glossary 37 Abbreviations 37 Terms 38 References 41 Appendix A Incremental Effects of Light Sources and Sign Sheeting on Legend Luminance for Overhead Guide Signs 44 Appendix B Assessment of Background Complexity Using Digital Images of Roadway Scenes by Image Processing 57 Appendix C Open-Road Study Details 62 Appendix D Guidelines for Nighttime Overhead Sign Visibility