Optimal Cycle-Length Formulas for Intersections With or Without Transit Signal Priority

Webster’s formula for optimal green split and cycle length is a common way to optimize signal settings at signalized intersections. However, these equations are intended to be used for optimizing signal timing plans for fixed-time isolated intersections, balancing phase utilization and minimizing car delay for undersaturated conditions. These formulas are less appropriate for near-saturated and oversaturated conditions because of the asymptotical behavior of the cycle-length formula when the intersection flow ratio approaches one. These formulas were not conceived for operation under transit signal priority (TSP) strategies. The main objective of this paper is to develop formulas for the optimal cycle length that can be applied when mild TSP strategies, such as green extension or green extension with phase rotation, are implemented or when the intersection operates under near-saturated or oversaturated conditions. A formula for optimal cycle length is developed as a function of lost time and intersection flow ratio. The formula is applicable both with and without TSP. It appears that for green split, no new formulas are required because the Webster equisaturation approach is close to optimal. The cycle-length formula is validated for undersaturated, near-saturated, and oversaturated conditions with and without TSP for two-, three-, and four-phase signalized intersections. Compared with Webster’s formula, the proposed formula shows a significant improvement in reducing person delay. Compared with Webster’s formula, average person delay is 6%, 17%, and 22% less and average bus delay is 16%, 27%, and 35% less for two-, three- and four-phase signalized intersections, respectively.

• Record URL:
  https://doi.org/10.3141/2558-08
• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/isbn/9780309441315
• Authors:
  • Wolput, Bart
  • Christofa, Eleni
  • Tampère, Chris M J
• Publication Date: 2016

Language

• English

Media Info

• Media Type: Print
• Features: Figures; References; Tables;
• Pagination: pp 78–91
• Monograph Title: Traffic Signal Systems, Volume 2
• Serial:
  • Transportation Research Record: Journal of the Transportation Research Board
  • Issue Number: 2558
  • Publisher: Transportation Research Board
  • ISSN: 0361-1981

Subject/Index Terms

• TRT Terms: Optimization; Traffic delays; Traffic oversaturation; Traffic signal cycle; Traffic signal priority; Traffic signal timing
• Subject Areas: Data and Information Technology; Highways; Operations and Traffic Management; Public Transportation; Safety and Human Factors; I70: Traffic and Transport;

Filing Info

• Accession Number: 01592101
• Record Type: Publication
• ISBN: 9780309441315
• Report/Paper Numbers: 16-1804
• Files: TRIS, TRB, ATRI
• Created Date: Feb 29 2016 4:56PM