Guidance for Left-Turn Flashing Yellow Arrow (FYA) Implementation in Nebraska

Authors

• Aemal Khattak, University of Nebraska-LincolnFollow
• Li Zhao, University of Nebraska-LincolnFollow
• Frank Selase Dzawu, University of Nebraska-Lincoln

ORCID IDs

0000-0002-6695-9842 (Khattak)

0000-0003-1914-1041 (Zhao)

0009-0000-6743-5728 (Dzawu)

Date of this Version

4-2026

Document Type

Article

Citation

Khattak, A., Zhao, L., and  Selase Dzawu, F. (2026). "Guidance for Left-Turn Flashing Yellow Arrow (FYA) Implementation in Nebraska", NDOT Research Report SPR-FY24(037).

Abstract

This research evaluates the safety performance of flashing yellow arrows (FYA) and driver behavioral responses in Nebraska, using data from 324 FYA intersections (Lincoln 160; Omaha 164) to develop evidence-based implementation guidance. The study addresses critical knowledge gaps in local driver acceptance patterns, the effectiveness of phasing configurations, and a comprehensive safety assessment that integrates crash and conflict analyses. The methodology employed four complementary analyses: (1) negative binomial crash frequency modeling of 3945 unique left turn crashes (2015-2024) across Lincoln and Omaha; (2) binary logistic regression of 948 gap acceptance decisions across 43 intersections; (3) linear regression of post-encroachment time for 613 completed left turns; and (4) detailed video investigation of 18 crashes at three Omaha intersections with lead-lag FYA phasing. Results demonstrate no statistically significant overall crash increase post-FYA installation when controlling for exposure (Lag: Incidence Rate Ratio [IRR]=0.937, p=0.364; Lead: IRR=1.027, p=0.563), though aggregate trends were influenced by five high-volume outlier intersections. Sensitivity analysis excluding outliers revealed lag phasing produced a statistically significant 15.1% reduction in crashes (IRR=0.849, p=0.038). Perceived Yellow Trap" (PYT) phenomenon, where lead-lag phasing configurations created perceptual confusion during phase transitions, accounting for 72% of observed crashes. Gap acceptance analysis showed lag phasing associated with 10% shorter critical gaps (3.85s vs. 4.28s), enabling higher operational efficiency. Recommended operational thresholds include prioritizing lag phasing at high-exposure locations, refining exposure thresholds using cross-product metrics, optimizing signal timing, and time-of-day operation. When properly implemented and following the recommended operational thresholds, FYA installation should improve intersection safety.