Guidelines for Left Turn Signal Phasing Options by Time of Day: A Safety and Operational Study

North Carolina has adopted the use of flashing yellow arrows (FYA) in many intersections across the state as a means of providing protected/permissive left turns while minimizing driver confusion that can accompany the operation. In 2014, North Carolina Department of Transportation (NCDOT) completed a study to develop crash modification factors (CMF) associated with the conversion of left turn protection at intersections to FYA. Since that study, additional information has become available including data regarding FYA at dual left turn lanes. This project plans to use that additional data to refine the CMFs developed by the department, in addition to answering new safety questions regarding FYA. In addition to this safety work, the project intends to develop guidelines for the implementation of permissive left turn phasing by time of day. Currently, for an intersection that has no safety restrictions (due to sight distance, opposing traffic speeds, etc.), the decision for implementing protected or permissive left turn phasing is based solely on vehicle volumes. When the only volumes available are for the peak period, it can be challenging to determine whether protected phasing should be extended to non-peak hours. Through the use of continuous count stations and spot intersection turning movement counts, the research team will develop methods to assist engineers in extrapolating the volumes for non-peak hours. From these volumes, guidelines will be developed to quantify the delay savings which can be expected by all users of the intersection if permissive phasing was implemented in off-peak hours. To assist in ensuring the guidelines are understandable and implementable by NCDOT staff, draft guidelines will be provided to select engineers along with sample data for a number of intersections. Engineers will be asked to follow the guidance and select a phasing plan for the left turn movements in question. The research team will use this feedback to improve the guidance.


  • English


  • Status: Active
  • Funding: $210,317
  • Contract Numbers:


  • Sponsor Organizations:

    North Carolina Department of Transportation

    Research and Development
    1549 Mail Service Center
    Raleigh, NC  United States  27699-1549
  • Managing Organizations:

    North Carolina Department of Transportation

    Research and Development
    1549 Mail Service Center
    Raleigh, NC  United States  27699-1549
  • Project Managers:

    Penny, Lisa

  • Performing Organizations:

    North Carolina State University, Raleigh

    Institute for Transportation Research and Education
    Campus Box 8601
    Raleigh, NC  United States  27695-8601
  • Principal Investigators:

    Warchol, Shannon

    Cunningham, Christopher

  • Start Date: 20170801
  • Expected Completion Date: 20200930
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01640064
  • Record Type: Research project
  • Source Agency: North Carolina Department of Transportation
  • Contract Numbers: FHWA/NC/2018-22
  • Files: RIP, STATEDOT
  • Created Date: Jun 29 2017 5:27PM