Citation

Sutula T, Mysz C. IMSA J. 2011; 49(5): 48-51.

Copyright

(Copyright © 2011, International Municipal Signal Association)

DOI

unavailable

PMID

unavailable

Abstract

This article describes how traffic signal professionals have been searching for a suitable method to implement lead-lag left turn phasing while retaining the operational benefits of protected/permissive left turn (PPLT) signal displays. The topic culminated with the publication of the National Cooperative Highway Research Project 3-54, (NCHRP 3-54), "Evaluation of Traffic Signal Displays for Protected/Permissive Left-Turn Control" and the publication of the 2009 Manual on Uniform Traffic Control Devices (MUTCD). Based on research results found in NCHRP 3-54, the 2009 MUTCD allows for the use of a four section left-turn signal display that incorporates a red left arrow, yellow left arrow, flashing yellow left arrow and a green left arrow. This type of signal is called the Flashing Yellow Arrow (FYA). Implementation of FYA operation in a traffic signal controller differs from traditional industry practice in that it introduces the requirement to output and monitor a fourth signal indication. This article is an overview of the two current common methods for monitoring FYA. The two current methods for implementing FYA are: (1) Green Separate Method; and (2) FYA Separate Method. This article provides information about specific issues that can arise when monitoring FYA with either of the two methods. When selecting one of these methods it is important to understand the difference between the two methods and the resulting impact on monitoring for conflicting signal displays.