Study Details

Study Title: Safety Effectiveness of Flashing Yellow Arrow: Evaluation of 222 Signalized Intersections in North Carolina

Authors: Simpson and Troy

Publication Date:JAN, 2015

Abstract: The purpose of this project is to develop crash modification factors (CMFs) for the implementation of Flashing Yellow Arrow (FYA) based on the specific before and after period conditions of a signalized intersection. Although this countermeasure has been used for years in North Carolina and other States, none of the published studies to-date have provided CMFs for left turn crashes specific to the treated approaches, and none have provided CMFs for the three-section FYA for permissive only left turns. Crash data from 222 intersections in North Carolina with FYA-protected/permissive left turn (FYA-PPLT) and/or three-section FYA-permissive only left turn installations were used to provide CMFs for five Category types: Category 1 (Permissive Only to FYA-PPLT), Category 2 (Protected Only to FYA-PPLT), Category 2A (Protected Only to FYA-PPLT with Time of Day 12 Operation), Category 3 (5-Section PPLT to FYA-PPLT), and Category 4 (Permissive Only to FYA-Permissive Only). A before and after crash analysis with consideration for traffic increase was used to determine the safety estimates. Safety performance functions were used to account for the effect of traffic volume trends. Readers may be most interested in Category 3 and 4, where the change is exclusive to the left turn display and not a change in phasing. All CMF results are statistically significant for Category 3, and target and injury CMF results are statistically significant for Category 4. Based on the results from our study sites, we find a statistically significant decrease in target left turn crashes and injury crashes when going from a solid green ball to a FYA for permissive left turns when phasing remains unchanged. This applies regardless of whether the left phasing is protected/permissive or fully permissive.

Study Citation: Simpson, C.L. and S.A. Troy. "Safety Effectiveness of Flashing Yellow Arrow: Evaluation of 222 Signalized Intersections in North Carolina". Presented at the 94th Annual Meeting of the Transportation Research Board, Paper No. 15-1593, Washington, D.C., (2015).


CMFs Associated With This Study

Category: Intersection traffic control

Countermeasure: Change from 5-section "doghouse" protected/permissive left turn to flashing yellow arrow protected/permissive left turn

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.9346.63 StarsAllAllNot specifiedNot specified
0.85314.73 StarsAllK,A,B,CNot specifiedNot specified
0.83816.23 StarsLeft turnAllNot specifiedNot specified
0.74725.33 StarsLeft turnK,A,B,CNot specifiedNot specified

Countermeasure: Change from permissive only to flashing yellow arrow permissive only

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.89210.82 StarsAllAllNot specifiedNot specified
0.68931.12 StarsAllK,A,B,CNot specifiedNot specified
0.49850.23 StarsLeft turnAllNot specifiedNot specified
0.34965.13 StarsLeft turnK,A,B,CNot specifiedNot specified

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.9356.52 StarsAllAllNot specifiedNot specified
0.65434.62 StarsAllK,A,B,CNot specifiedNot specified
0.59840.23 StarsLeft turnAllNot specifiedNot specified
0.59240.82 StarsLeft turnK,A,B,CNot specifiedNot specified

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

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.124-12.42 StarsAllAllNot specifiedNot specified
1.206-20.62 StarsAllK,A,B,CNot specifiedNot specified
3.684-268.42 StarsLeft turnAllNot specifiedNot specified
4.778-377.82 StarsLeft turnK,A,B,CNot specifiedNot specified

Countermeasure: Change from protected only to flashing yellow arrow protected/permissive left turn with time of day operation

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.9019.93 StarsAllAllNot specifiedNot specified
0.9267.42 StarsAllK,A,B,CNot specifiedNot specified
2.732-173.22 StarsLeft turnAllNot specifiedNot specified
2.371-137.12 StarsLeft turnK,A,B,CNot specifiedNot specified