The use of detection to activate protected left-turn phasing has developed primarily through empirical trial and error and has been instituted without the supporting scientific theory. This study compared the performance of left-turn phasing to provide quantifiable benefits of one phasing over another. Permitted, protected, and protected/permitted (P/P) phasing are analyzed for a range of left-turn volumes and opposing through traffic in order to develop relational curves. The measure of left, through and overall intersection delay is used to compare the different phasing performances. Specific consideration is given to determining the optimal location of the queue detector for P/P phasing. From the analysis, guidelines are developed for determining the type of left-turn phasing based on left-turn volume, opposing through volume and lane geometry. The analysis indicates that P/P phasing provides the best method of left-turn phasing signal control. The P/P phasing allows for a wide range of control and is better able to accommodate the changing volumes throughout the day. The optimal queue detector location for P/P varies based on opposing volume and geometry. The Utah Department of Transportation (UDOT) typically has placed the queue detector location at the third vehicle. This is based on permitted phasing to accommodate two sneakers per cycle. Therefore the third vehicle location triggers the protected phasing so that all left-turning vehicles can be accommodated. However, this assumes that no gaps exist in the oncoming traffic to provide capacity for left turns and that the opposing traffic is operating near capacity. Based on this assumption, delay comparisons indicate that geometry and queue locations are related. For a single lane geometry, the third vehicle location is appropriate. However, as the geometry is increased to two or three lanes, the opposing through volume increases and the overall intersection delay is reduced when the detector location is moved to the fourth vehicle location.


  • English

Media Info

  • Media Type: Digital/other
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 114 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00748690
  • Record Type: Publication
  • Report/Paper Numbers: MPC Report No. 98-91,, UDOT Report UT-96.08,, UTRG-0697-05
  • Created Date: May 8 1998 12:00AM