Impacts of Left-Turn Traffic Signal Phasing Strategies on Safety Outcomes

Left-turn (LT) maneuvers are among the most challenging and highest-risk movements at signalized intersections. Transportation agencies across the United States have adopted varied signal phasing and operational strategies to manage LT movements, such as Flashing Yellow Arrow (FYA) displays in lieu of the Solid Green Ball for permissive turns, and FYA used in place of or in combination with protected-only phasing. While prior studies have examined safety performance at regional or whole-intersection levels, limited information exists at the intersection-approach level, where phasing decisions are actually implemented. This project develops a methodology for approach-level safety analyses at signalized intersections based on left-turn signal phasing and operational strategies, focusing on crash involvement and outcomes in the vicinity of signalized intersections. The methodology quantifies and compares safety outcomes across locations, time periods, and operational strategies (e.g., before-and-after conditions; peak versus off-peak periods) using crash frequencies, severity outcomes, and exposure-adjusted rates, with analytical techniques including non-parametric statistical tests. Application is demonstrated through a Las Vegas metropolitan area case study, drawing on crash records from Nevada Department of Transportation (NDOT) and local agencies; signal, roadway, and traffic characteristics from the RTC of Southern Nevada; and vehicle trajectory and operational data (e.g., Streetlight, INRIX) from regional partners. Results will advance the state of the science and practice for approach-level LT safety analysis and provide transportation agencies a basis to refine policies and procedures that enhance safety and operational efficiency at signalized intersections.

Language

• English

Project

• Status: Active
• Funding: $194,920.00
• Contract Numbers:

  69A3552348323

• Sponsor Organizations:

  Office of the Assistant Secretary for Research and Technology

  University Transportation Centers Program
  Department of Transportation
  Washington, DC  United States  20590
• Managing Organizations:

  Howard University

  2400 6th Street, NW
  Washington, DC  United States  20059
• Project Managers:

  Bruner, Britain

• Performing Organizations:

  University of Nevada, Las Vegas

  Las Vegas, NV  United States 
• Principal Investigators:

  Nambisan, Shashi

• Start Date: 20260803
• Expected Completion Date: 20270504
• Actual Completion Date: 0
• USDOT Program: University Transportation Centers

Subject/Index Terms

• TRT Terms: Case studies; Crash rates; Crash severity; Left turns; Safety analysis; Signalized intersections; Traffic signal phases
• Geographic Terms: Las Vegas Metropolitan Area
• Subject Areas: Highways; Operations and Traffic Management; Safety and Human Factors;

Filing Info

• Accession Number: 01999931
• Record Type: Research project
• Source Agency: Research and Education for Promoting Safety (REPS) University Transportation Center
• Contract Numbers: 69A3552348323
• Files: UTC, RIP
• Created Date: Aug 19 2026 4:02PM