Signal Priority near Major Bus Terminal Case Study of Ruggles Station, Boston, Massachusetts

tem, the signal returns to a background cycle (2). For example, in many applications priority requests are simply inhibited for a certain number of cycles or minutes after a priority interruption so as to ensure that other phases recover. This kind of blunt strategy limits the potential effectiveness of signal priority. Further complicating matters, buses turning into and out of a terminal tend to belong to minor traffic streams not favored by arterial coordination plans and with long red periods. Where buses are part of the main arterial traffic flow, bus priority often benefits general traffic. In contrast, giving priority to buses by using minor phases can be detrimental to intersection capacity and, by interrupting coordination, risk queue spillback, hurting following buses as well as general traffic. In addition, buses often approach the terminal from conflicting directions, so that priority given to one bus may delay another. Finally, the intersections near major bus terminals are often near saturation, offering little slack that priority logic can take advantage of. Two cities in Europe with a reputation for aggressive transit priority underscore the challenge of giving signal priority near a terminal. Zurich’s (Switzerland) trams experience nearly zero delay at most signalized intersections (3), with one notable exception: turning into and out of terminals, where conflicting tram lines with high frequency interfere with one another. And in Eindhoven, Netherlands, highly aggressive signal priority logic results in nearly zero delay for late buses at most intersections (4); however, no priority is applied where buses turn into and out of the central station. This research addresses the questions: How effective can signal priority be near a major bus terminal? What signal priority strategies are likely to be most effective there? Because the answers can be very site specific, a case study approach is used, modeling traffic around Boston’s Ruggles Station through microsimulation to see to what extent, at least in one case, giving priority to buses at traffic signals can reduce bus delay.