ASSESSMENT OF MULTIPLE LEFT-TURN PHASING STRATEGIES

Left-turn movements at an intersection affect the capacity of that intersection. As the left-turning volume at an intersection continues to grow, the green time required to meet the left-turn demand increases. This, in turn results in longer cycle lengths. Also with the increase in the left-turn volume, the queues lengthen resulting in greater storage length requirements. The combinations of these effects tend to increase delay at the intersection and lower the level of service. Installation of multiple left-turn lanes (dual and triple) can result in the reduction of vehicle queue lengths, delays and left-turn storage length. In Missouri, multiple left-turns are gaining popularity. However, the installation of these multiple left-turns raises questions for which the Missouri Department of Transportation (MoDOT) has not yet developed answers. Specifically, MoDOT seeks guidance on: criteria for determining when to install double and triple left-turns; the type of phasing to be used for dual and triple left-turn lanes; whether to use "Dallas" or permitted lead-lag phasing for any left-turn lanes; and where to begin reducing the number of receiving lanes downstream of an intersection with multiple left-turn lanes. Based on the current practices being followed by various state DOTs and from the review of literature, the following recommendations are being made: (1) Capacity analysis should be used to determine the set of conditions for upgrading left-turn lanes from single to dual and dual to triple; (2) If it is not feasible to perform capacity analysis due to a lack of resources, the following rules of thumb may be used for determining the point of upgrade: when left-turning volume is greater than or equal to 300 vph, upgrade from single to dual left-turn lane, and when left-turning volume is greater than or equal to 600 vph, upgrade from dual to triple left-turn lane; (3) Protected only phasing should be used for dual and triple left-turn lanes; (4) "Dallas" phasing should be used instead of lead-lag protected + permissive phasing for single left-turn lanes along with R10-12a (combined R10-10L and R10-12) sign to avoid confusion to the adjacent through traffic; and (5) For downstream lane drop distance, consider the solution by Shen as shown in Table 2 of this report.

• Record URL:
  https://spexternal.modot.mo.gov/sites/cm/CORDT/RDT04003.pdf
• 
• Record URL:
  https://rosap.ntl.bts.gov/view/dot/37850
• Corporate Authors:

  University of Missouri, Rolla

  Department of Civil, Architectural and Environmental Engineering
  1870 Miner Circle
  Rolla, MO  United States  65409-0030

  Missouri Department of Transportation

  Research, Development and Technology, 1617 Missouri Boulevard
  P.O. Box 270
  Jefferson City, MO  United States  65102

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Qureshi, M
  • Spring, G
  • Malkayigari, V R
  • Rathod, J
• Publication Date: 2003-12

Language

• English

Media Info

• Media Type: Digital/other
• Features: Appendices; Figures; References; Tables;
• Pagination: 46 p.

Subject/Index Terms

• TRT Terms: Exclusive phasing; Lane drops; Lead-lag phasing; Left turn lanes; Left turn phase; Level of service; Literature reviews; Recommendations; State of the practice; Traffic delays; Traffic queuing; Traffic volume
• Uncontrolled Terms: Dual left turn lanes; Triple left turn lanes
• Geographic Terms: Missouri
• Subject Areas: Highways; Operations and Traffic Management; Research; I73: Traffic Control;

Filing Info

• Accession Number: 00970451
• Record Type: Publication
• Report/Paper Numbers: RDT 04-003,, RI 02-014,, Final Report
• Files: NTL, TRIS, USDOT, STATEDOT
• Created Date: Mar 12 2004 12:00AM