Transit Signal Priority (TSP) is an operational strategy that facilitates the faster movement of transit vehicles at signalized intersections. The implementation of TSP makes transit vehicles experience less delay at intersections due to increase in green time or reduction in red time based on the priorities employed. By reducing control delay at signalized intersections, TSP can improve schedule adherence and travel time efficiency. Reducing transit travel times reduces operation cost for any transit agency. Through TSP, buses may be given priority at traffic signals either all the time or under conditions like lateness and/or number of passengers on the vehicle.
TSP is made of four components. A detection system delivers vehicle data including arrival time and approach. This system is commonly Global Positioning System (GPS) based but can also be roadside detectors. The detection system then requests priority from the traffic control system through communication with a priority request generator. Priority control strategies are then used to process requests and decide how to grant priority. Finally there is the TSP system management software that manages the system, collects data, and generates reports.
TSP treatments can be categorized into four types and are passive priority, active priority, conditional active priority and adaptive priority. Passive priority is one of early TSP methods which simply provide adjusted signal timing based on transit travel times. Active priority systems comprise a transit vehicle sensor located upstream of an intersection approach that requests signal priority call and a signal controller. When a transit vehicle approaches the sensors, the signal controller provides the designated TSP strategies (early green, green extension, red truncation etc.) for predetermined durations.
Conditional active priority is an advanced version of active priority in which Intelligent Transportation System provides more capabilities to support sophisticated TSP control. Under this treatment, priority is granted to transit vehicles that meet certain conditions based on the deviation of the vehicle from the schedule or time elapsed since last awarded priority. Additional mechanisms are to be installed to safely operate these treatments. These may involve AVL systems for measuring schedule adherence, APC systems for measuring transit vehicle occupancy.
Adaptive priority refers to relatively new generation of priority schemes which seeks to achieve advanced operational objectives such as improving transit headway regularity, reducing total vehicle delay along the corridor and maximizing person throughput by means of adaptive signal control. Under this preferential treatment, the traffic signal controller adjusts its plan dynamically according to the criteria reflecting the desired objective. This treatment offers considerable promise for maximizing the benefits for both transit vehicles and regular traffic.