Effect of Large Vehicles on Left Turn Gap Acceptance at Signalized Intersections

Critical and follow-up headways are the foundation for estimating the saturation flow of permissive left turns at signalized intersections. Current critical and follow-up headways recommended in the 2016 Highway Capacity Manual (HCM) are based on limited data collected from five intersections in Texas in the 1970s. This study analyzed over 2,500 left-turning vehicles at 45 intersection approaches, provides insights into gap acceptance parameters, and evaluates the effect of different site-specific factors. Video data were collected and processed from different geographical regions in the United States—Arizona, Florida, North Carolina, Virginia, and Wisconsin. Using the Maximum Likelihood method to estimate gap acceptance parameters, the mean critical headway was 4.87 seconds and the mean follow-up headway was 2.73 seconds. The mean critical headway for large vehicles was 6.03 seconds. To account for site-specific characteristics, the effect of several geometric and operational variables on critical and follow-up headway were explored. Through a meta-regression analysis, the posted speed limit and width of opposing travel lanes were found to have a significant effect on gap acceptance parameters. Results showed that with decreasing posted speed limit and width of opposing lanes, critical and follow-up headways also decrease resulting in greater saturation flows. When site-specific saturation flow estimates are compared with HCM saturation flow estimates, the differences ranged from -30% to +23%. This research quantifies and illustrates the impact of site-specific characteristics on gap acceptance parameters and saturation flow.

• Record URL:
  • http://safersim.nads-sc.uiowa.edu/final_reports/UW-2-Y4_Final%20Report.pdf
• 
• Supplemental Notes:
  • This document was sponsored by the U.S. Department of Transportation, University Transportation Centers Program.
• Corporate Authors:

  University of Wisconsin, Madison

  Department of Civil and Environmental Engineering
  1415 Engineering Drive
  Madison, WI  United States  53706

  Safety Research Using Simulation University Transportation Center (SaferSim)

  University of Iowa
  Iowa City, IA  United States  52242

  Office of the Assistant Secretary for Research and Technology

  University Transportation Centers Program
  Department of Transportation
  Washington, DC  United States  20590
• Authors:
  • Noyce, David A
  • 0000-0001-5887-8391
  • Chitturi, Madhav
  • 0000-0003-0580-3454
  • Claros, Boris
  • 0000-0002-4787-1749
• Publication Date: 2021-5

Language

• English

Media Info

• Media Type: Digital/other
• Edition: Final Research Report
• Features: Figures; Photos; References; Tables;
• Pagination: 41p

Subject/Index Terms

• TRT Terms: Gap acceptance; Headways; Left turns; Signalized intersections; Traffic flow
• Subject Areas: Highways; Operations and Traffic Management; Safety and Human Factors;

Filing Info

• Accession Number: 01848015
• Record Type: Publication
• Report/Paper Numbers: UW-2-Y4
• Contract Numbers: 69A3551747131
• Files: UTC, TRIS, ATRI, USDOT
• Created Date: Jun 6 2022 4:54PM