Section 2: Preempted Traffic Signals

Maintenance and Operations

Various settings in the traffic signal controller must be verified for compliance with the operation of the traffic signal controller and the preemption form (TxDOT Form 2304) for which the circuit was designed. The following
checks are recommended
 when inspecting a traffic signal for preemption:
  • Controller delay time matches what is shown on preemption form (line 1).
  • If delay time is used, memory
    must be
     set to non-locking, so controller does not accept false calls from the railroad company.
  • Minimum green time during preemption right of way transfer matches what is shown on preemption form (line 5).
  • Yellow change and red clearance times during preemption right of way transfer after track clearance green and after transitioning out of preemption
    cannot be
     less than what is programmed for normal operation of the signal for any phase (when signal is not under preemption) per Section 4D.27 of the TMUTCD.
  • Yellow change and red clearance times during preemption right of way transfer match what is shown on the preemption form (lines 7 and 8).
  • Pedestrian walk time matches preemption form (line 11).
  • Pedestrian clearance time matches preemption form (line 12).
  • Track clearance green time matches preemption form (line 51).
  • Track clearance, dwell/limited cycle and exit phases programmed properly in controller.
  • If train passes through crossing, verify that track clearance green does not terminate prior to the gates going down.
  • If gate down circuit is used and train passes through crossing, confirm that track clearance green terminates when gates go down and gate down preempt becomes active.
  • Any changes made to signal timings
    are documented
     in logbook in traffic signal controller.
  • Preemption form and traffic signal layout design sheets are available in the cabinet.
  • A warning label is present in the housing indicating the presence of the interconnection and that the cabling shall not be tampered
    with
     or disconnected.
  • Battery back-up system is connected and functioning properly.
  • Interconnection conductor and conduit functional.
Railroad companies are required to test preemption circuits monthly. Although the district railroad coordinator would not typically be present with the railroad company to verify the advanced preemption time is correctly functioning from the railroad company, the timing settings in the controller should be verified from time to time to verify the preemption is functioning as designed on the preemption form.
This can occur on an as-needed basis or as part of the annual joint preemption test outlined in Chapter 7.

Traffic Signal Design Changes

Another common concern involves traffic signal timing modifications due to changes in speed limits or lane configurations. Ultimately, if changes are made, the yellow change and red clearance times during preemption cannot be less than what is programmed for normal operation of the signal for any phase. If the yellow change and red clearance times increase under normal operation, the times must also increase under preemption and other time during preemption must be sacrificed. This could typically occur by reducing delay time, minimum green time during right of way transfer, pedestrian timing during right of way transfer, or separation time and would require the preemption form be updated by the district railroad coordinator.
If a traffic signal is upgraded to accommodate pedestrian movements, the preemption setup should also be evaluated to see if pedestrians should be considered during preemption.
Finally, any changes to a roadway intersection adjacent to a railroad crossing should be coordinated with the affected railroad company. This includes work performed off railroad right of way to ensure no traffic impacts to the railroad crossing or preemption setup.