Evaluation of the Flashing Yellow Arrow Permissive-Only Left-Turn Indication Field Implementation (2008)

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ACKNOWLEDGMENT This work was sponsored by the American Association of State Highway and Transportation Officials (AASHTO), in cooperation with the Federal Highway Administration, and was conducted in the National Cooperative Highway Research Program (NCHRP), which is administered by the Transportation Research Board (TRB) of the National Academies. COPYRIGHT PERMISSION 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, FTA, Transit Development Corporation, or AOC 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. DISCLAIMER The opinion and conclusions expressed or implied in the report are those of the research agency. They are not necessarily those of the TRB, the National Research Council, AASHTO, or the U.S. Government. This report has not been edited by TRB. ii

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iv TABLE OF CONTENTS Author Acknowledgments ...........................................................................................................................vi Abstract .......................................................................................................................................................vii Executive Summary ...................................................................................................................................viii Chapter 1 – Background ............................................................................................................................... 1 Introduction .............................................................................................................................................. 1 NCHRP Project 3-54/Report 493 ............................................................................................................. 1 Problem Statement.................................................................................................................................... 3 Objective................................................................................................................................................... 7 Scope ........................................................................................................................................................ 7 Chapter 2 – Research Approach.................................................................................................................... 8 Research Tasks ......................................................................................................................................... 8 Task 1 – Literature Review ...................................................................................................................... 8 Task 2 – Agency Contact and Data Collection......................................................................................... 8 Evaluation Data .................................................................................................................................... 8 Study Database..................................................................................................................................... 9 Comparison Site Data......................................................................................................................... 11 Task 3 – Field Data Collection ............................................................................................................... 11 Task 4 – Data Analysis........................................................................................................................... 11 Grouped Analysis............................................................................................................................... 12 Task 5 – Report of Findings ................................................................................................................... 17 Chapter 3 – Literature Review.................................................................................................................... 18 FYA Literature ....................................................................................................................................... 18 Driver Eye Movement Evaluation .......................................................................................................... 18 Simultaneous Permissive Left-Turn Indications .................................................................................... 20 Two Allowable Permissive Left-Turn Indications ................................................................................. 22 Driver Comprehension of Solid Yellow Indication................................................................................ 22 Applications of the FYA in Separated Left-Turn Lanes......................................................................... 23 Driver and Pedestrian Comprehension of Requirements for Permissive Left-Turns ............................. 24 Driver Simulation............................................................................................................................... 25 Static Driver Evaluation ..................................................................................................................... 26 Static Pedestrian Evaluation............................................................................................................... 26 Experimentation with Three-Section Signal Displays............................................................................ 27 Literature Review Summary................................................................................................................... 29 Chapter 4 – Findings & Applications ......................................................................................................... 30 Research Results..................................................................................................................................... 30 Data Availability..................................................................................................................................... 30 Study Sites .............................................................................................................................................. 30 Sign Test Results .................................................................................................................................... 35 Linear Trend Analysis ............................................................................................................................ 41 Empirical Bayes Method Statistical Analysis Results............................................................................ 45 Regression Results.................................................................................................................................. 46 Chapter 5 – Installation Methods for FYA Signals..................................................................................... 52 FYA Indication Installation .................................................................................................................... 52 170E Controller Setup ............................................................................................................................ 52 NEMA TS-2, Type 2 Controller Setup................................................................................................... 52 Chapter 6 – Conclusions & Discussion....................................................................................................... 57 Discussion............................................................................................................................................... 57 Group A: Protected/Permissive Left-Turn Control ................................................................................ 57

v Group B: Converted from Protected Left-Turn Control......................................................................... 58 Future Evaluations.................................................................................................................................. 58 References................................................................................................................................................... 60 Appendix A – FHWA Interim Approval Memorandum ..........................................................................A-1 Appendix B – Conditions Report..............................................................................................................B-1 Appendix C – Intersection Inventory of Treatment Sites .........................................................................C-1 Appendix D – Traffic Volume Summary Tables......................................................................................D-1 Appendix E – Intersection Inventory of Comparison Sites ...................................................................... E-1 Appendix F – Table Summary of Grouped Evaluation Data .................................................................... F-1 Appendix G – Table Summary of Sites Not Included in Group Evaulation .............................................G-1

vi AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 20–7, Task 222 by the Traffic Operations and Safety Laboratory at the University of Wisconsin at Madison (UW- Madison). The Board of Regents of the University of Wisconsin System was the contractor for this study, with Charles Hoffman serving as Fiscal Administrator. David A. Noyce, Ph.D., P.E., Associate Professor of Civil Engineering at UW-Madison, was the Project Director and Principal Investigator. The other authors of this report are Casey R. Bergh, Research Assistant and M.S. Candidate at UW-Madison, and Jeremy R. Chapman, Research Assistant and Ph.D. candidate at UW-Madison. Dr. Rick Nordheim of the Department of Statistics at the University of Wisconsin-Madison provided support and review of the statistical analysis. The work was done under the general supervision of Professor Noyce at UW-Madison.

vii ABSTRACT The primary objective of this research was to evaluate the safety of the flashing yellow arrow (FYA) permissive only left-turn indication field installations. The ability of the FYA indication to improve safety was evaluated with respect to crash experience. Findings of the crash analysis were interpreted with respect to other variables such as signal phasing, vehicle flow rates, posted speed limits, and intersection geometry. The scope of this research included all known installations of the FYA prior to the commencement of this research. Data were limited to that which was made available by traffic engineers in locations where the FYA has been implemented, along with selected data that were directly obtained by the researchers. Findings were drawn from the analysis of 50 intersections in which the left-turn FYA indication was installed. Safety was improved at intersections that operated with protected/permissive left-turn (PPLT) phasing prior to field implementation of the FYA permissive only indication. Safety was not improved at intersections that operated with protected only left-turn phasing prior to field implementation of the FYA indication with PPLT phasing. The change in signal phasing had a more significant impact on safety than the change in permissive indication. No conclusions could be made at intersections that operated with permissive only left-turn phasing prior to implementation of the FYA indication, due to a minimal number of implementation sites and data. The results showed that the installation of the FYA indication for permissive left-turns provided a safety improvement when added to existing PPLT signal phasing operations.

viii EXECUTIVE SUMMARY Accommodating left-turn movements at signalized intersections provides a challenge to traffic engineers. In order to complete a left-turn at a signalized intersection, the driver must either find an appropriate gap in the opposing traffic stream or have all conflicting traffic stopped. As a result of this conflict of movements, successfully accommodating left-turn and opposing through movement vehicles is critical to the safe and efficient operation of signalized intersections. Traffic engineers use different phasing schemes within the signal cycle, namely permissive only, protected, or a combination of both phases, to accommodate left-turn movements at signalized intersections. Permissive only left-turn phasing allows vehicles to complete a left-turn during the green phase after yielding to opposing through traffic and pedestrians. Protected left-turn phasing provides right-of-way to the left-turn vehicle during a specified green phase in which a green arrow indication is displayed. Protected/permissive left- turn phasing uses both left-turn phases in the same signal cycle, as a leading, lagging, or lead-lag protected/permissive left-turn (PPLT) phase, depending on whether the protected phase precedes or follows the opposing through traffic in sequence. A comprehensive research study, titled “Evaluation of Traffic Signal Displays for Protected/Permissive Left-Turn Control,” was completed in 2003 for The National Cooperative Highway Research Program (NCHRP) as Project 3-54. The corresponding report, NCHRP Report 493, presented the findings of an extensive array of studies conducted to evaluate all currently used permissive only left-turn indications. Traffic engineers around the country had implemented a variety of unique permissive only left-turn signal indications in an attempt to better communicate to the left-turn driver that they must yield to opposing through traffic before turning. It was perceived that drivers did not adequately comprehend the predominant permissive only display in use, the circular green (CG) permissive only left-turn indication, because of increases in left-turn crashes and decreases in operational efficiency. Therefore, a number of unique permissive only left turn indications were implemented in an attempt to resolve the problem including the flashing red arrow (FRA), flashing circular red (FCR), flashing yellow arrow (FYA), and flashing circular yellow (FCY). Research was needed to evaluate each of these and determine which was most effective and could be uniformly applied throughout the United States (U.S.). To complete this research, a comprehensive array of research studies and experiments were completed including driver behavior laboratory analyses, operational and behavioral field evaluations, and full-scale driving simulator analyses. NCHRP Report 493 recommended the use of a flashing yellow arrow indication as the desired permissive only indication when using protected/permissive left-turn (PPLT) signal phasing. The report cited that the flashing yellow arrow had a high level of driver comprehension, overcame many of the human factors issues with permissive only left-turns, and was shown to have the most versatile characteristics of all the permissive only displays studied. Furthermore, the FYA had an important safety characteristic; drivers who did not understand the meaning of the FYA tended to yield, which is a desirable failure outcome. This was in contrast to drivers who did not understand the meaning of the CG, in which case drivers tended to assume right-of-way and go, a very undesirable outcome. After the conclusion of the NCHRP 3-54 research, a number of traffic engineers around the U.S. considered implementing a FYA permissive only indication. Between January 1, 2004

ix and March 20, 2006, the Federal Highway Administration (FHWA) approved numerous ‘Requests for Experimentation’ allowing a widespread implementation of the FYA. Additionally, between March 20, 2006 and the date of this report, the FHWA has granted permission for further implementations of the FYA under an ‘Interim Approval’ designation. Despite several research studies and experiments that were recently completed after NCHRP Report 493, questions remain as the FYA implementation continues. Specifically, a question remains as to how the implementation of the FYA has impacted the safety of the nearly 300 intersections which now use a FYA permissive only left-turn indication. Therefore, a need exists to quantitatively evaluate the safety of the intersections implemented with the FYA indication and to qualitatively document the experiences of each implementation agency. A greater understanding of the safety (crash experience) and driver behavior before and after the installation of the FYA will greatly assist traffic engineers as they consider incorporating the FYA into the transportation system. The primary objective of this research was to evaluate the safety effectiveness of the FYA permissive left-turn indication field installations. The ability of the FYA indication to improve safety was evaluated with respect to crash experience. Findings of the crash analysis were interpreted with respect to other variables such as signal phasing, vehicle flow rates, posted speed limits, and intersection geometry. The scope of this research included all known installations of the FYA prior to the commencement of this research. Data were limited to that which was made available by traffic engineers in locations where the FYA has been implemented, along with selected data that were directly obtained by the researchers. Five tasks were included in the study design. These tasks included extensive amounts of data collection, working with traffic engineers at each location to obtain the necessary information, and a statistical analysis of the data obtained. Of the nearly 300 intersections reportedly implementing the FYA indication, documentation and data was only available for approximately 120 locations throughout the U.S. at the time of this research. These sites represent a widely varied cross-section of intersection types and sizes. None of the intersections in which the FYA indication was implemented was without some selection bias or without some change in operating conditions before and after the installation. Furthermore, none of the sites in which traffic engineers provided data where complete or comprehensive in terms of obtaining all desirable data for analysis. Nevertheless, the affects of a change in left-turn phasing and/or the implementation of the FYA indication were analyzed. This research resulted in three general conclusions: • Safety was improved at intersections that operated with PPLT phasing prior to field implementation of the FYA permissive indication with PPLT phasing. • Safety was not improved at intersections that operated with protected only left-turn phasing prior to field implementation of the FYA permissive indication with PPLT phasing. • No conclusions could be made at intersections that operated with permissive only left- turn phasing prior to implementation of the FYA indication, due to a minimal number of implementation sites and data. The installation of the FYA indication at sites which currently operate PPLT signal phasing showed improvements in safety. In other locations, the change in left-turn signal

x phasing had a more significant impact on safety than the change in left-turn indication, although safety appeared to improve with time. Information was also provided related to traffic signal controller logic and the physical installations of the FYA installation.