A traffic control strategy was designed explicitly to accommodate bus priority on Avenida Ponce de Leon between Old San Juan and the northern terminus of the metro, Tren Urbano, now under construction in Puerto Rico. Up to 36 buses operate per hour in mixed traffic northbound and in an exclusive contraflow lane southbound. The control strategy is characterized as "highly interruptible" because it responds quickly to, and recovers quickly from, priority interruptions, which are expected to occur frequently. It features full actuation and schedule-based conditional priority for buses. Buses may request to pass through the intersection or to advance to the bus stop that may be occupied by a standing queue. Priority tactics include green extension, early green, and early red. To preserve capacity and encourage dwell time to overlap with traffic delay, bus blockage at a stop forces an early and minimum length red. There is no background cycle; however, loose progression is provided by means of requests, of lower priority than bus requests, from upstream intersections to force or hold green until a platoon arrives. The control strategy was programmed and tested with VISSIM, whose useful features and weaknesses for this study are described. The results indicate significant transit travel time savings without slowing general traffic compared with the existing strategy of fixed time control with progression.
Abstract