Four-Quadrant Gate (4QG) Exit Gate Management System

What is EGMS?

The EGMS (Exit Gate Management System) is designed to perform exit gate timing and control as a part of an overall Four-Quadrant Gate Warning System (4QG). The EGMS utilizes self-checking inductive loop detectors to determine the presence of vehicles within the area between the entrance gates and exit gates (Minimum Track Clearance Distance – MTCD). With the EGMS, if a vehicle is detected within the MTCD, the exit gates will not be lowered until the vehicle clears the MTCD to avoid trapping vehicles within the crossing. As a backup mode, automatic changeover to timed exit gate or exit gate fail-up mode in the event of inductive loop failure is available through front panel programming. The EGMS is designed to fully conform with current AREMA standards and safety critical design principles. EGMS is provided with a touch-sensitive LCD (liquid crystal display) to allow data entry and access to all stored data. Operation is through intuitive menus with buttons added and removed as necessary to simplify operation.

Why Four-Quadrant Gates?

To limit motorists’ violation of two-quadrant gate warning systems, the 4QG Crossing System is utilized to provide a full closure to the crossing. Typical two-quadrant gate systems utilize gates to prevent approaching vehicles from entering the crossing (entrance gates). The problem arises when vehicles drive around the lowering or lowered entrance gates either because they do not see the train or feel that they can beat the train to the crossing. The Federal Railroad Administration (FRA) has reviewed studies from across the country and analyzed the effectiveness of various types of grade crossing signal improvements. According to the FRA, four-quadrant gates have an effectiveness rating higher than any other type of active grade crossing warning device improvement. Many cities desiring quiet zones have turned to four-quadrant gates as the most effective means of silencing train horns through their respective communities.

Dynamic Exit Gate Operation

Each exit gate may be held in or forced to the vertical position based on detection of vehicles within the crossing area (MTCD). If no vehicles are present within the MTCD when the warning system is activated, the exit gates will descend simultaneously with the entrance gates. Any vehicle present within the MTCD when the warning system is activated will cause the exit gate toward which the vehicle is moving to remain vertical or, if lowering, to return to vertical. Once the vehicle(s) clear(s) the MTCD, the exit gates will be driven down. Through the system configuration data, the exit gates can be configured for fail-up or fail-down operation, so that the removal of power to the gate mechanism will cause the exit gates to rise to the vertical position or lower to the horizontal position in accordance with the design standards of the railroad.

Timed Exit Gate Operation

For isolated crossings where vehicular traffic is unrestricted from exiting MTCD, exit gates may be selected to lower following a preset time (exit gate clearance time - EGCT) in lieu of vehicle presence detection.

System Flexibility

Timed mode may be installed where dynamic mode is not currently required, but may become necessary in the future. The change may be effected through by plugging in the loop processor modules, connecting the roadway loops and changing the EGMS system database.

System Monitoring

EGMS provides two levels of system health. The first level confirms the functional status of the vehicle detection system. In the event of a detector failure, the dynamic exit gate operation is disabled and operation continues with exit gates operating in timed mode or fail-up as programmed and a detection health output is set false. The second level of health monitoring is derived based on the functionality of the entire system. If any entrance gate fails to reach the full horizontal position within a pre-programmed maximum time, the exit gates are raised. This prevents the possibility of vehicle entrapment in cases of entrance gate malfunction or broken gate arms. Additional elements of the EGMS system are monitored as well including exit gate failure to raise, improper gate position, excessive gate raise or lower time and general system health. Any operational fault will result in the second level health output being set false. The EGMS health outputs are usually connected to a warning system recorder or remote alarm reporting system to facilitate maintainer response in the event of trouble. EGMS stores all event is an internal data log available for easy viewing by maintenance personnel through simple keystrokes.

Inductive Loop Operation

One of the major elements of the EGMS is the integral Self-Checking Loop Processor. The loop processor modules slide into the EGMS chassis and allow for easy setup using a menu driven display. The inductive loop technology has been used for years in both vehicular traffic control and rail applications. Recent advances in microprocessor circuitry and the ability to self check operation of the loop processor have made the inductive loop one of the most reliable vehicle detection technologies available today. Individual loops are also sequentially scanned to eliminate “crosstalk” between adjacent loops. With the addition of railroad-standard safety critical design techniques, the Self-Checking Loop Processor provides outstanding reliability along with self-check and failure detection.

Loop placement depends upon the number of tracks and the number of vehicular traffic lanes at the crossing. Loops are required between the entrance gate and first track, between the last track and the exit gate, and between each track. Depending on lane configurations, a single loop may be used to cover multiple lanes, or one or more loops may be used for a single lane. Separate sets of loops are required for each direction of travel. Loops are available in any size and are factory assembled and pre-tested or available as wire on a spool for site specific applications.

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