Accommodating left turns at signalised intersections has been a challenge for traffic engineers as they seek balance between two conflicting goals; capacity and safety. The use of a four-section head for the left-turn lane only with a flashing yellow arrow indication for permissive left turns has been deemed to be the new standard for signalization. With the advent of this new signal configuration, there was the opportunity to take the protected-permitted left-turn mode to a new level of operation. Although numerous studies have developed warrants and guidelines for selecting left-turn control types, to date there are no clear or uniform standards for the implementation of a variable left-turn mode, changing by time-of-day. Hence, there is a need to develop an interactive and efficient framework to serve as a decision support system (DSS) for the evaluation of left-turn phasing alternative based on intersection conditions. This framework will allow (1) an interactive evaluation of left-turn phasing and ultimately recommend phasing mode by time-of-day and (2) Traffic Management Center (TMC) data to be fed into the DSS so that intersections requiring attention/modification of left-turn mode can be flagged. The current study develops an interactive DSS for assessing the likely benefits of warranting a permitted left-turn phase using custom design approach. The developed DSS is designed to predict these benefits based on multilevel factorial parameters that are practical and applicable to assist TMCs in evaluating the efficiency of a permitted left-turn phase by time of day. (Author/publisher)
Abstract