Safety and Operations Assessment of Various Left-Turn Phasing Strategies

This research evaluated the safety and operational impacts of different left turn movement treatments at signalized intersections. The project (1) compared the safety and operational impacts of protected-only left-turn (POLT) phasing with those of protected-permissive left-turn (PPLT) phasing with a flashing yellow arrow (FYA) indication, (2) compared the safety and operational impacts of doghouse displays with those of four-section vertical displays for PPLT with an FYA, and (3) identified whether time-of-day (TOD) variable left-turn control mode with an FYA produces confusion among left-turning drivers. The literature showed that converting a POLT to a PPLT control mode is associated with an increase in crash rates while reducing intersection delay. Previous research has recommended selecting the control mode on the basis of traffic volumes, speed limit, sight distance, number of lanes, and crash history. Previous research has shown that doghouse displays are associated with larger crash modification factors, more confusion among drivers, and higher delays than a four-section vertical display with an FYA. The results of our driver comprehension survey showed that half of the drivers who had encountered intersections with a left-turn control mode variable by TOD felt confused by that phasing strategy. On the other hand, the simulation-based analysis showed that changing the left-turn control mode by TOD yields more efficient traffic operations and lower average delays.

  • Record URL:
  • Supplemental Notes:
    • This document was sponsored by the U.S. Department of Transportation, University Transportation Centers Program.
  • Corporate Authors:

    Washington State University, Pullman

    Department of Civil and Environmental Engineering
    Pullman, WA  United States  99164-2910

    Washington Department of Transportation

    Transportation Planning Department
    Olympia, WA  United States  98504-5201

    Pacific Northwest Transportation Consortium

    University of Washington
    More Hall Room 112
    Seattle, WA  United States  98195-2700

    Office of the Assistant Secretary for Research and Technology

    University Transportation Centers Program
    Department of Transportation
    Washington, DC  United States  20590
  • Authors:
  • Publication Date: 2018


  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Project Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 123p

Subject/Index Terms

Filing Info

  • Accession Number: 01709112
  • Record Type: Publication
  • Contract Numbers: DTRT13-G-UTC40
  • Created Date: Jun 10 2019 10:11AM