OPTIMIZATION OF LEFT LANE TRAFFIC SIGNALS

The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the information presented herein. This document is disseminated under the sponsorship of the Department of Transportation, University Transportation Centers Program, in the interest of information exchange. The U.S. Government assumes no liability for the contents or use thereof. 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 compares 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