The purpose of the controller testing is to allow TxDOT and the railroad an opportunity to test the traffic signal system and verify that the preemption programming is operating as designed while in a controlled environment. Controller testing may take place at the signal shop or the manufacturer’s facilities as needed. The testing should occur 2-4 weeks prior to the planned cutover but may occur as late as a day before if proposed operations are standard. Representatives from both TxDOT and the railroad, as well as any consultants as needed, should be present for the controller testing.

During controller testing, the Traffic Signal Representative shall complete Sections 1-3 and 5 of Form 2625 to verify traffic signal operations. A note should be added to the beginning of Section 4 stating the form is for controller testing. Section 4 cannot be filled out without railroad participation. Controller testing shall follow the testing procedures defined in the Form 2625 Instructions except the obstructed gate down test (Box 49) which will need to be simulated by removing the input to the controller. Boxes 50 and 51 cannot be completed during controller testing.

A controller testing packet may also be prepared by the railroad and/or the railroad traffic consultant for all participants. The controller testing should evaluate all potential railroad relay inputs, any potential fault conditions, and any potential errors in the traffic signal preemption timing or programming. Both the expected and the actual response of the systems should be noted for each scenario. If the actual response does not match the expected response, the participants shall adjust the preemption timing and/or programming as necessary to match and document any changes. TxDOT should schedule additional testing, if necessary, to demonstrate that the overall system will perform as intended.

The failure states and their programmed responses should be fully assessed during the controller testing. If any equipment malfunctions, the failure state assists in ensuring the safety of any users at an interconnected crossing while providing some traffic flow. Some generic failure states and responses are outlined below. Refer to Chapter 5, Section 4 for more details regarding standard preemption operations:

Crossing Relay (XR) Failure – truncate the walk and pedestrian clearance phases, if active. Then transition to Preemption Clearance Interval (PCI) until minimum time is reached, and then to all-red flash. If a maximum preemption timer is not programmed, the controller will remain in PCI until the issue is resolved (Preemptor 3).
Gate-Down (GD)/Island (ISLR) Relay Failure (Form 2625, Box 48) – if a pedestrian phase is active, then the traffic signal will truncate the walk and pedestrian clearance phases. The signal will then transition to PCI until maximum interval is reached, and then to all-red flash. If a maximum preemption timer is not programmed, the controller will remain in PCI until the issue is resolved. Note, in most cases, the island relay will terminate PCI and transition the traffic signal to the dwell phases. This failure would only occur if there were an issue with the island circuit. (Preemptor 4)
Supervised Relay Failure (Form 2625, Box 49) – if a pedestrian phase is active, then the traffic signal will truncate the walk and pedestrian clearance phase. The signal will transition to PCI until minimum interval is reached and the GD input is received, and then enter and remain in limited-service operation. (Preemptor 1)

The controller testing shall also verify the expected traffic signal controller response to a preemption call and how the traffic signal transitions to preemption operations. Refer to Chapter 5, Section 4 for standard preemption operations and the Form 2625 Instructions for testing procedures. In most scenarios in which a malfunction occurs, the traffic signal controller would be expected to truncate any active walk and pedestrian clearance intervals then transition the active vehicular phase to yellow, red clearance, and PCI. After the PCI completes, the traffic signal will transition to all-red flash until any issues are resolved. The preemptor should be programmed for monitor flash to allow for network notifications.