Transit Signal Priority

About TSP

Transit Signal Priority (TSP) is considered to be one of the popular transit management strategies that can be used to help transit service become more reliable, faster, and more cost-effective. TSP has little impact on general traffic and is a relatively inexpensive way to make transit more competitive with the automobile. Transit signal priority modifies the normal signal operation process to accommodate transit vehicles better. RTD acknowledges TSP as one of the advanced tools to improve bus speed and reliability. Consequently, RTD developed a new TSP operating concept, and the designed TSP concept has been deployed at 18 intersections in the district to improve transit service and performance.

TSP Concept of Operations

Typically, TSP operation allows traffic signal controllers to skip conflicting signal phases, to shorten conflicting phases, to lengthen compatible phases, or to modify phase sequence to serve the transit vehicle. Two primary TSP strategies are 1) Green Extension and 2) Early Green (Red Truncation). More specifically:

• A green extension strategy extends the green time for the TSP movement when a TSP-equipped transit vehicle is approaching. The green extension is one of the most effective forms of TSP since a green extension does not require additional clearance intervals.
• An early green strategy shortens the green time of the preceding phases to expedite the return to green (i.e., red truncation) for the movement where a TSP-equipped vehicle has been detected. This strategy only applies when the signal is red, and a TSP-equipped vehicle is approaching. Both green extension and early green strategies are available together within TSP enhanced control environment but are not applied to the same signal cycle.

RTD TSP System Architecture

After assessing the state of the practice, recent experience and modern communications technology available for the bus TSP design, RTD developed a unique TSP approach by utilizing RTD’s cellular communications technology to implement TSP operation. The most significant advantage over other methods studied is that this approach fully utilizes the bus on-board equipment and system software that RTD has been applying to CAD/AVL and Automatic Passenger Counting (APC) systems. The CAD/AVL system generally detects real-time bus locations to activate and deactivate TSP requests. The figure below demonstrates the standard TSP system. When a bus approaches a TSP-equipped intersection, CAD/AVL detects that and then checks the bus location against the bus's scheduled timetable and bus loading in real-time. If the bus is behind schedule and the bus load reaches a predefined level, a TSP request will be sent to the traffic controller owned and maintained by the partnering agency to activate the TSP routine.

TSP Application Reference Materials and Contact Info

An "RTD Transit Signal Priority (TSP) Application Guidelines" has been prepared and published. The application guidelines explain what TSP is, why it is important, what the benefits are, and the important issues surrounding the topic. This report contains the steps one should follow to implement a TSP project in the district successfully. To request a copy of the report or have any other Transit Priority questions (e.g., TSP, Queue Jump, Bus Bypass), please email [email protected].