Active-Style Interface Specification

General
The traffic signal system shall provide a solid-state, modular interface. Optimum functionality and safety features are achieved when the modules are installed in a standalone companion input file rack with module insertion verification protection. The companion input file rack shall provide two to four slots for the preemption system modules. Unless otherwise stated, the contractor shall furnish a standalone companion input file rack with module insertion verification protection for the railroad preemption. The interface shall function as follows:
  • The railroad preemption system shall operate from nominal 120 Vac power applied via the companion input file rack or the input file pins.
  • Each interconnection circuit to the railroad warning system shall operate on 24 Vdc and be isolated from all traffic signal cabinet internal voltage sources, AC line, grounds or AC neutral.
  • The railroad preemption system shall generate the isolated 24 Vdc supply for the interconnection circuits.
  • Each input from the railroad shall be optically isolated from other inputs and not referenced to any traffic signal cabinet internal voltage sources, AC line, grounds or AC neutral.
  • The railroad preemption system shall provide a Traffic Signal Health isolated output. This output shall be an isolated 12 Vdc and shall be energized when Traffic Signal Health as described below is valid. The system shall monitor the 120 Vac load switch signal bus control circuit. In addition, the system shall monitor an appropriate signal output to sense “soft flash” operation. Soft Flash is flashing operation generated by the controller unit by providing outputs to the load switches that are turned off and on to develop the specific flash pattern. These two inputs shall be referenced to 120 Vac Neutral. If the signal bus becomes de-energized or flashing operation is sensed, the system shall de-energize the Traffic Signal Health output to the railroad.
  • The railroad preemption system shall provide outputs referenced to controller unit logic ground for selection of programmed functions.
Supplemental Terminals
All supplemental terminals provided as a part of the railroad preemption interface shall utilize a "cage-clamp" design, such as manufactured by WAGO Corporation or equivalent. Terminals which provide "side wipe" connections or set screws are not acceptable. Terminal shall provide a minimum of 25 slots for railroad inputs.
Preemption System Isolator Modules
Each module providing preemption outputs shall be a processor-based unit. At least one module shall incorporate an organic light-emitting diode (OLED) display to indicate unit status, inputs, outputs and system timing. Modules shall be provided with an internal power supply to operate from the 120 Vac source. The combined railroad preemption interface system, including all modules, shall provide the following functions and features:
For preemption outputs and health monitoring:
  • Input for 120 Vac signal bus (load switch power).
  • Input for 120 Vac flashing signal indication for soft flash sense (soft flash indication).
  • 12 Vdc isolated output to drive railroad vital relay for Traffic Signal Health.
  • Isolated option input for Preemption Clearance Interval(s) monitoring from traffic signal load switch outputs.
  • Input isolation for Advance Preemption, Supervised, Crossing Active and Gate Down from railroad warning system.
  • Isolated option for Advance Pedestrian Preemption (APP), Gate Up, Island from railroad warning system.
  • Outputs (six) for the traffic signal controller unit to select preemption plans.
  • Output (advance) for control of blank-out signs or other devices.
  • Output (simultaneous) for control of blank-out signs or other devices.
For operation of blank-out signs:
  • 120 Vac load switch circuitry for an input file rack
  • 4 Isolated circuits
  • Ground true input provides 120 Vac output
  • LED output channel status
  • Self-supplied 24 Vdc to module rack
Railroad Preemption Isolator Module Input File Rack
The input file rack provides slots for the railroad preemption system isolator modules. The input file rack shall provide module insertion verification relay protection on the processor module slot(s) to verify proper seating. An improperly seated or missing module will place a call to the traffic signal controller preemption plan programmed for flash operation.
Unless otherwise specified, the railroad bungalow shall be provided with isolated relay contacts for the interface. Solid state outputs from the railroad may be used as an option to the relay contacts as required by the railroad. The interface shall provide the circuits described as required and specified in the preemption interconnection design.
At interconnected traffic signals, the controller assembly shall provide the operation detailed below relative to the railroad preemption functionality and operation.
The controller assembly shall be provided with all hardware, software and firmware necessary to provide the operation described herein. The designer, contractor and/or traffic signal technician should closely review the functional requirements of the railroad preemption operation to assure that the equipment is capable of performing the functions as specified. In many cases, the railroad circuits have been designed to provide and support the specific functionality. As a result, no exceptions will be permitted to these requirements. The Traffic Management Section of the Traffic Operations Division (TRF-TM) should be contacted for any further clarification regarding the hardware specifications.