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(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| 0.934 | 6.6 |  | All | All | Not specified | Not specified |
| 0.853 | 14.7 | | All | K,A,B,C | Not specified | Not specified |
| 0.838 | 16.2 | | Left turn | All | Not specified | Not specified |
| 0.747 | 25.3 | | Left turn | K,A,B,C | Not specified | Not specified |
Countermeasure: Change from permissive only to flashing yellow arrow permissive only
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| 0.892 | 10.8 |  | All | All | Not specified | Not specified |
| 0.689 | 31.1 | | All | K,A,B,C | Not specified | Not specified |
| 0.498 | 50.2 | | Left turn | All | Not specified | Not specified |
| 0.349 | 65.1 | | Left turn | K,A,B,C | Not specified | Not specified |
Countermeasure: Change from permissive only to flashing yellow arrow protected/permissive left turn
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| 0.935 | 6.5 | | All | All | Not specified | Not specified |
| 0.654 | 34.6 | | All | K,A,B,C | Not specified | Not specified |
| 0.598 | 40.2 | | Left turn | All | Not specified | Not specified |
| 0.592 | 40.8 | | Left turn | K,A,B,C | Not specified | Not specified |
Countermeasure: Change from protected only to flashing yellow arrow protected/permissive left turn
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| 1.124 | -12.4 | | All | All | Not specified | Not specified |
Countermeasure: Change from protected only to flashing yellow arrow protected/permissive left turn with time of day operation
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| 0.901 | 9.9 | | All | All | Not specified | Not specified |
| 0.926 | 7.4 | | All | K,A,B,C | Not specified | Not specified |
