An Analysis of Decision Boundaries for Left-Turn Treatments

The purpose of this project is to evaluate the safety and operational differences between three left-turn treatments: permitted, protected, and protected-permitted left-turn phasing. Permitted phasing allows vehicles to turn left after yielding to any opposing vehicles; protected phasing provides an exclusive phase for vehicles to turn left that does not allow opposing vehicles; and protected-permitted phasing combines the previous phasing alternatives, allowing vehicles to turn after yielding while also providing some green time for protected left-turns. As part of evaluating the differences between these left-turn treatments, crashes before and after the change at intersections that had experienced a permanent change from one phase alternative to another were compared. A general increase in total crashes was observed for most intersections, and an increase in left-turn crashes per million entering vehicles was also observed in intersections that had experienced a change from protected to protected-permitted phasing; no other clear trends were observed. The research team also gathered simulated data using VISSIM traffic modeling software and safety data were extracted from these simulations using the Surrogate Safety Assessment Model (SSAM) to identify decision boundaries between each left-turn treatment. Equations were derived using the simulated data; these equations were then charted and final decision boundaries were developed for the 1-, 2-, and 3-lane configurations between permitted and protected-permitted phasing as well as between protected-permitted and protected phasing.

• Record URL:
  https://drive.google.com/file/d/10cF6-GE70p9h_Yfjmol7cTmuHGGYsUrZ/view?usp=sharing
• 
• Record URL:
  https://rosap.ntl.bts.gov/view/dot/42386
• Corporate Authors:

  Brigham Young University

  Department of Civil and Environmental Engineering
  Provo, UT  United States  84602

  Utah Department of Transportation

  Research Division
  Salt Lake City, UT  United States  84114-8410

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Schultz, Grant G
  • Adamson, Michael L
  • Stevens, Michael D
  • Saito, Mitsuru
• Publication Date: 2019-4

Language

• English

Media Info

• Media Type: Digital/other
• Edition: Final Report
• Features: Figures; References; Tables;
• Pagination: 102p

Subject/Index Terms

• TRT Terms: Before and after studies; Crashes; Exclusive permissive phasing; Exclusive phasing; Left turns; Permissive phasing; Signalized intersections; Traffic safety
• Identifier Terms: Surrogate Safety Assessment Model; VISSIM (Computer model)
• Geographic Terms: Utah
• Subject Areas: Highways; Operations and Traffic Management; Safety and Human Factors;

Filing Info

• Accession Number: 01707846
• Record Type: Publication
• Report/Paper Numbers: UT-19.05, R0402310
• Contract Numbers: 18-8736
• Files: NTL, TRIS, ATRI, USDOT, STATEDOT
• Created Date: Jun 12 2019 3:31PM