SELECTION CRITERIA FOR LEFT-TURN PHASING AND INDICATION SEQUENCE

The development of guidelines and recommendations for the selection of left-turn phasing and indication sequences at signalized intersections is documented in this paper. The guidelines developed are based on field studies and use easy-to-obtain data for the selection process. A simple three-level decision process regarding the most suitable left-turn phasing treatment to be used is established. The process favors the least restrictive permissive left-turn phase unless traffic and geometric conditions warrant the more restrictive protected/permissive or protected-only phasings. These guidelines are based on threshold values designed to determine what constitutes an excessive value for any particular variable, beyond which more restrictive left-turn phasing treatments may be justified. The guidelines developed also reflect a selection process that recognizes the trade-off between operational efficiency and safety. The study shows that selection of a particular phase is a multiobjective process involving a number of factors, and in many cases more than one condition must be met to justify the selection of a particular phase that will ensure an optimal solution.