Safety at highway grade crossings long has been a concern of railroads, rail-transit properties and government at local, state and federal levels. At issue are impatient motorists who circumvent down crossing gates in an attempt to drive over the crossing before the arrival of a train. This frequently meets with fatal results to motorists and train crews. These concerns are especially acute in high-speed rail territory, where grade separation of highways and railways is not possible - and where the speed of the train makes it nearly impossible for the train operator to stop the train once the crossing comes into view and a motor vehicle stalled on the crossing becomes visible. To address these concerns and to attempt to improve grade-crossing safety for both motor vehicles and trains, particularly at high-speed locations, US&S has developed the Four-Quadrant Gate Highway- Crossing Warning System.
With the US&S Four-Quadrant Gate Highway-Crossing Warning System, the grade crossing is treated as an interlocked junction between two rights-of-way, the street and the railroad track. The system primarily consists of four highway-crossing signal/gate assemblies, an inductive motor-vehicle detection loop, a vital/nonvital processor, a cab signal system interface in rail territory equipped with cab signaling, and approach and island track circuits. Gate operation is controlled so that motor vehicles will not be trapped on the crossinduring the approach of a train.
Signal/Gate Assemblies
Two Model 95 signal/gate assemblies are installed on each side of the track so the highway is completely blocked on both sides of the rail right-of-way when the gates are down and a train is approaching the crossing. These gate mechanisms are mounted on the signals installed on the exit-side of the crossing (the side through which a motor vehicle must pass when leaving the crossing) and are designed to raise should power to the highway-crossing warning system fail. The entrance gates during such a circumstance will fall to the down position. This mitigates the possibility of a motor vehicle being trapped on the crossing by a down gate blocking the crossing location's exit-side lane.
Loop Detectors
Loop detectors are buried beneath the crossing surface for detecting motor vehicles. Since the loop detectors' inductance varies whenever a motor vehicle passes over the crossing, the presence of a motor vehicle on the crossing will be detected. The loop output is sent to the warning system's vital/non-vital processor. If a vehicle is on the crossing when a train approaches and activates the highway-crossing warning system, the exit gates will remain raised to allow the vehicle to exit the crossing. Once again, this feature provides an exit for the vehicle so it's not trapped on the crossing by all four gates being down.
MicroLok ® II Vital/Non-Vital Processor
The US&S MicroLok II Wayside Control System functions as a vital/non-vital processor, and serves as the heart of the control system. It executes the vital logic required for gate operation, motor-vehicle detection, and the locomotive cab indications (VMI in cab signal territory) that alert the train engineer of a motor vehicle (or other obstruction) on the crossing. This processor also tests for loop-detector faults, crossing-system intrusion and broken gates, and, if any of these conditions are detected, it generates a maintenance call.
Track Circuits
Track circuits detect the presence of a train within the crossing approaches and on the island (where track and road meet) and initiate operation of the highwaycrossing warning system.
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