ACCOMMODATING PEDESTRIANS IN SPLIT PHASING

Split phasing is a type of signal phasing scheme, which separates vehicle conflicts by assigning the right-of-way sequentially to the two opposing approaches. Split phasing is often used when the intersection geometric layout would no allow the two left-turn movements on the opposing approaches to move simultaneously, or on an approach with a shared left/through lane. Such an intersection geometric layout may be a result of a need to serve specific traffic flow patterns. An example of this is when two left-turn lanes are needed but the budget of right0f-way constraints would not allow having tow exclusive left-turn lanes. The left-turn demand is better served by using an exclusive left-turn lane plus a shared left/through lane. From a safety and capacity point of view, the two opposing left-turn movements have to be separated by using a split-phasing scheme. Previous research has been focused on analyzing vehicle conflicts with respect to various left-turn phasing schemes. These studies have investigated the effect of various left-turn controls on potential conflicts between the left-turn vehicles and the opposing through vehicles. However, studies on pedestrian timing as well as the efficiency of traffic operations under split phasing operations are somewhat limited. There are a number of issues related to split phasing and pedestrian timing treatment. In order for a driver unfamiliar with an intersection to understand that he or she has a protected movement, a left turn arrow must be displayed. However, the display with left turn arrows would require serving the pedestrians on each crosswalk in two sequential phases, which could significantly affect the efficiency of signal operations. The purpose of this paper is to address these various issues related to split phasing and pedestrian timing considerations. A new split phasing scheme called Protected/Permitted Left Turns is proposed for achieving the maximum efficiency but yet maintaining safety.