Study Details

Study Title: Approach-Level Safety Comparison of Permissive-Protected and Protected Left Turn Phasing to Flashing Yellow Areas

Authors: Shea and Medina

Publication Date: 2018

Abstract: Since the introduction of flashing yellow arrow (FYA) indications in the MUTCD, transportation agencies have increasingly adopted this alternative to improve left-turn operations. However, it has not been until recently that agencies have accumulated enough data (both temporally and spatially) to conduct safety evaluations of FYA implementations for specific types of “before” left-turn phasing. Most past studies have focused on intersection-level crash analyses given the difficulties to obtain reliable crash data at the level of a single approach where the direction of travel, particularly for left turn movements, should be individually verified. This study aims at bridging research gaps by estimating the change in target (left-turn related) crash frequencies, specifically for approaches converted from a permissive-protected or a protected-only left-turn operation to a permissive-protected FYA indication. Safety performance functions for permissive-protected, protected only, and the FYA approaches are estimated. In addition, crash modification factors for converting permissive-protected to FYA, and for converting protected-only to FYA are presented. Results from this approach-level analysis support some of the findings from previous studies conducted at intersection-level.

Study Citation: Shea, M., and J. Medina. "Approach-Level Safety Comparison of Permissive-Protected and Protected Left Turn Phasing to Flashing Yellow Arrows". Presented at the 97th Annual Meeting of the Transportation Research Board, Paper No. 18-06742, Washington, D.C., (2018).

Study Report: Download the Study Report Document

CMFs Associated With This Study

Category: Intersection traffic control

Countermeasure: Change from protected only to flashing yellow arrow protected/permissive left turn

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
3.428-242.83 StarsLeft turnAllNot specifiedNot specified

Countermeasure: Change from protected-permissive to flashing yellow arrow protected-permissive on approach

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.97782.222 StarsLeft turnAllNot specifiedNot specified