Study Details

Study Title: Safety Performance Evaluation of Flashing Yellow Arrow: Time-of-Day vs 24-hour Operations

Authors: Zhang et al.

Publication Date:JAN, 2023

Abstract: The flashing yellow arrow (FYA), as the permissive left-turn indication, has been widely implemented to mitigate driving confusion caused by the permissive steady green indication. The selection of an appropriate FYA operation type, however, remains an open-ended question as few studies have evaluated the safety effectiveness of FYA under different operation types, that is, 24-hour, time-of-day (TOD), and switching from 24-hour to TOD. Moreover, since FYA has been typically used at intersections with a single left-turn lane, its safety effectiveness at intersections with dual left-turn lanes has not been well investigated. To bridge these gaps, this paper focuses on evaluating the safety effectiveness of FYA at intersections with varying numbers of left-turn lanes under different operation types and examining whether the FYA operation type switch affects safety performance. Empirical Bayes before/after studies are conducted for 24-hour, TOD, and switching from 24-hour to TOD FYA operation types using multivariate adaptive regression splines models in comparison with traditional negative binomial models. Safety performance functions are developed for different combinations of crash types and a different number of left-turn lanes. Results show that for intersections with either a single left-turn lane or dual left-turn lanes, 24-hour and TOD FYA operation types reduce crashes by 8.76% to 50%. However, intersections with dual left-turn lanes experience a 31.2% increase in total crashes when switching from 24-hour to TOD FYA operation type, while intersections with a single left-turn lane see a 60% decrease in rear-end crashes.

Study Citation: Zhang, X., X. Li, and Y-J. Wu. "Safety Performance Evaluation of Flashing Yellow Arrow: Time-of-Day vs 24-hour Operations". Presented at the 102nd Annual Meeting of the Transportation Research Board, Paper No. 23-04250, Washington, D.C., (2023).

Related Citations: Zhang, X., X. Li, and Y-J. Wu. "Safety Performance Evaluation of Flashing Yellow Arrow: Time-of-Day vs 24-hour Operations". Transportation Research Record No. 2677(7), Transportation Research Board of the National Academies of Science, Washington, D.C., (2023).

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Intersection traffic control

Countermeasure: Changing left turn phasing from protected-permissive to flashing yellow arrow (FYA)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.85154 StarsLeft turnAllAllUrban and suburban
0.82184 StarsAngleAllAllUrban and suburban
0.7304 StarsAllK,A,B,CAllUrban and suburban
0.68324 StarsLeft turnAllAllUrban and suburban
0.65354 StarsAllK,A,B,CAllUrban and suburban
0.69314 StarsLeft turnAllAllUrban and suburban
0.61394 StarsAllK,A,B,CAllUrban and suburban
0.73274 StarsAllAllAllUrban and suburban
0.65354 StarsLeft turnAllAllUrban and suburban
0.6404 StarsAllK,A,B,CAllUrban and suburban
0.52484 StarsLeft turnAllAllUrban and suburban
0.58424 StarsAllK,A,B,CAllUrban and suburban
1.1-104 StarsLeft turnAllAllUrban and suburban
0.4604 StarsRear endAllAllUrban and suburban
1.34-344 StarsLeft turnAllAllUrban and suburban