NCHRP 3-54: Evaluation of Traffic Signal Displays for Protected/Permissive Left-turn Control

KAI led a nine-year national research effort to identify a uniform traffic signal display for protected/permissive left-turn (PPLT) signals. The research project, originally sought by the American Association of State Highway and Transportation Officials (AASHTO), was funded by the National Academy of Sciences through the National Cooperative Highway Research Program (NCHRP). KAI developed a research plan to identify the traffic signal indication for the (PPLT) control that would provide the “best” overall safety and operational benefits to the public. Subsequent to these initial scoping efforts, KAI, in conjunction with the Texas Transportation Institute, the University of Massachusetts at Amherst, the University of Wisconsin, and Siemens ITS developed and refined NCHRP 3-54. The objective of the NCHRP 3-54 project was to evaluate the safety and effectiveness of different signal displays and phasing for protected/permissive left-turn control through laboratory and field studies. The research project investigated multiple existing left-turn signal displays in use across the United States and ultimately led to the recommendation to implement an entirely new Flashing Yellow Arrow signal display nationwide. The Flashing Yellow Arrow display provides a universally understood means of communicating when a left-turn signal is allowed and offers safety advantages to all. Unlike previous research efforts that had been completed in a laboratory setting, the project team coordinated, supervised, and reported on the field implementation of Flashing Yellow Arrow in cooperation with six volunteer agencies located around the county. Based on the findings of these additional studies and the previously prepared research work, a final report (NCHRP Research Report 493) was published in 2003 that includes recommendations for uniform display(s) for protected/permissive left-turn control. Subsequently, the project team continued working with NCHRP and the National Committee on Uniform Traffic Control Devices (NCUTCD) through the summer of 2004 to advance implementation of the project recommendations, including participation in NCUTCD task force meetings and review of draft language revisions to the Uniform Vehicle Code that set the stage for national implementation of the Flashing Yellow Arrow.