The source graphic, a Windows Metafile (WMF), for the TSD can be downloaded here:
The following discusses how the National ITS Architecture provides the transportation service described by this service package. Each numbered item describes the operation of that portion of the service package identified with the corresponding number on the transaction set diagram.
The market package describes two concepts for transit vehicle signal priority. In the first the Transit Vehicle Subsystem (TRVS) communicates directly with the Roadway Subsystem (RS) to request that priority be given at the approaching intersection (local signal priority request). The signal priority system is monitored and controlled at a high level by the Transit Vehicle Driver (transit vehicle operator display and transit vehicle operator inputs). (Note that for safety reasons, in general, the vehicle operator should not be notified if the vehicle is behind schedule or if signal priority is being requested or given. Conversely, if the vehicle is ahead of schedule (aka "running hot"), the driver may be notified to "wait" only while the vehicle is stopped and the door is open.) The TRVS might also make its decision on whether to request the priority based upon a set of business rules regarding the status against its schedule, or the schedule of connecting routes. The flow transit schedule information from the TRMS could provide real time schedule information that would be used in making the decision regarding the real-time request for a priority. The intersection controller grants the priority based upon pre-established criteria and then informs the TMS that priority has been given (in the flow right-of-way request notification).
In a more advanced concept for transit vehicle signal priority, the TRMS receives location and schedule performance information from the TRVS (transit vehicle schedule performance). Based on interaction with the Transit Operations Personnel (transit operations personnel inputs and transit operations status), the TRMS makes the decision to request signal priority from the TMS at one or more upcoming intersections on the route (traffic control priority request). The TMS grants the signal priority (signal control commands, sent from the TMS to the RS), monitors signal controller status on the route (with the flow signal control status and signal fault data), and informs the TRMS of its actions (traffic control priority status).