All-Red Clearance Intervals for Use in the Left-Turn Application of Flashing Yellow Arrows

Abstract

In recent years, agencies across the United States have embraced the implementation of the flashing yellow arrow (FYA) for permissive left turns. Previous research determined that the FYA indication communicated the presence of permissive left turns more effectively compared with the circular green, which led to its inclusion in current guidelines. Despite the recent implementations and multiple research efforts to investigate the operations of FYA permissive indications, there remains a lack of national guidance on the definition of change and clearance intervals for transitioning between protected and permissive left turns at intersections operating permissive/protected left turns. This study investigates the connection between traditional signal phasing/design and human factors through both a driver comprehension computer-based static evaluation and a real-world field study to evaluate various practices employed across the United States. Overall, the survey results provide evidence to suggest similar comprehension levels between the FYA and circular green (CG) permissive left-turn indication sequences. The field evaluation yielded similar comprehension levels; however, drivers appeared to induce fewer potential conflicts when the all-red clearance interval was present. Initial evidence suggests potential safety benefits associated with including the all-red clearance interval upon transitioning between the protected and permissive left-turn phase with the application of a FYA.