Safety Effects of Protected and Protected/Permitted Left-Turn Phases

Protected left-turn phases at signalized intersections are intended to reduce the frequency of angle collisions that result from conflicts between left-turning vehicles and opposing through vehicles. The American Association of State Highways and Transportation Officials (AASHTO’s) “National Cooperative Highway Research Program (NCHRP) 500 series” also notes that the frequency of rear-end and sideswipe crashes between left-turning vehicles and following through vehicles can also be reduced with properly timed, protected left- turns. Various studies have demonstrated the overall safety effectiveness of protected left-turn phases (e.g., Harkey et al., 2008; Davis and Aul, 2007). A consensus on the extent of this safety effectiveness under different intersection conditions does not exist. While separate left-turn phasing may reduce delay for left-turning vehicles, it may increase the overall intersection delay and disrupt traffic progression. It is therefore important to understand the safety effects of protected left-turn phases under a variety of intersection conditions so that appropriate operational and safety trade-offs can be quantified and considered by agency decision makers. Protected/permitted left-turn phasing is sometimes used as a compromise between fully-protected and permitted only phasing. Information on the safety effects of protected/permitted under a variety of intersection conditions is needed as well. This project will estimate the safety effects of protected and protected/permitted left-turn phases for different intersection conditions. Intersection conditions of interest may include factors such as turning volumes, opposing through volumes, pedestrian crossing volumes, approach speeds, sight distance, number of lanes, and type of channelization.


  • English


  • Status: Completed
  • Funding: $95000
  • Contract Numbers:


  • Sponsor Organizations:

    Research and Innovative Technology Administration

    University Transportation Centers Program
    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Managing Organizations:

    Mountain-Plains Consortium

    North Dakota State University
    P.O. Box 6050, Department 2880
    Fargo, ND  United States  58108-6050
  • Project Managers:

    Kline, Robin

  • Performing Organizations:

    University of Utah, Salt Lake City

    College of Engineering, Department of Civil Engineering
    Salt Lake City, UT  United States  84112-0561
  • Principal Investigators:

    Medina, Juan

  • Start Date: 20150731
  • Expected Completion Date: 20190731
  • Actual Completion Date: 20191104
  • USDOT Program: University Transportation Centers Program
  • Source Data: MPC-495

Subject/Index Terms

Filing Info

  • Accession Number: 01579919
  • Record Type: Research project
  • Source Agency: Mountain-Plains Consortium
  • Contract Numbers: DTRT13-G-UTC38
  • Files: UTC, RiP
  • Created Date: Oct 27 2015 4:48PM