Railroad control systems

Railroad control systems

Those devices and systems used to direct or restrain the movement of trains, cars, or locomotives on railroads, rapid-transit lines, and similar guided ground-transportation networks. Such control varies from the use of simple solenoid valves to fully automatic electronic-electromechanical systems.

A primary function of railroad control systems is to ensure the safe movement of trains. This is generally accomplished by providing train operators and track-side operators with visual indications of equipment status. The simplest form of control consists of track-switch-position indicators combined with track-side manually operated “stop” or “proceed” signals, which the train operator follows. Advanced systems incorporate fully automated train control, subject to human supervisory control and potential intervention when faults occur in automated systems. See Control systems, Railroad engineering, Traffic-control systems

Block signaling significantly improves the safety of railroad operations. Automatic block signaling is accomplished by sectionalizing the track into electrical circuits to detect the presence of other trains, engines, or cars. Logic circuits in the control system detect the locations of the trains and the positions of switches, and then set the necessary signals to inform the train operators when to stop, run slowly, or proceed at posted speeds. The control system automatically detects the presence of a leading train, selects the signal to be given, and then sets the signal indications for the following train operators to read so that they may perform accordingly. In conjunction with automatic block signals, many subway rapid-transit lines incorporate automatic trip stops along the tracks to ensure that train operators obey the stop signals.

Automatic cab signaling systems display signaling information (traditionally, permitted speeds) on board the train. Coded information is transmitted to the train, generally via the running rails. Antennas and receivers aboard the train pick up, amplify, decode, and distribute the intelligence, which then causes the proper signal aspects to be displayed in the cab. Automatic cab signaling reduces or eliminates the need for wayside signals and improves the all-weather capability of trains and the train-handling capacity of the track.

Automatic train control (ATC) subsystems, located wholly on board the train, sense whether or not the train is operating within safe speed limits. If it is not, automatic train control sets the brake to bring the train to a stop or to a speed below the allowed speed. Automatic cab signaling with automatic train control is used on many railroads and several rapid-transit lines in the United Sates and on systems in Europe and Japan. Automatic train operation (ATO) subsystems perform nonvital operating functions such as starting, running at the prescribed speeds, slowing down, and stopping, and on some rapid-transit installations include passenger-door controls. Automatic train operation builds upon the information transmitted to the train as part of automatic cab signaling, and is a logical next step in automating train operations.

Station stopping presents a special set of requirements for rapid transit, commuter railroads, and mainline railroad passenger operations. Accurate positioning of car doors at the station platform and smooth deceleration at relatively high rates are desirable for passenger comfort and efficient operating performance. A special subsystem of control referred to as programmed train-stop systems (or station-stop systems) are a combination of on-board and wayside electronic and electromechanical equipment that can bring a train to rest within inches of its stopping-point target.

Car identification systems is an example of central line supervision. This system scans and decodes a series of colored and patterned lines placed on the side of each car to identify an individual car. This information is transmitted to the operations area, where a computer system is used to establish routing, determine maintenance schedules, and so on. Dispatchers and central operators can also use computer workstations to obtain information on system status.

Railroad terminals (points of origin and destination of trains) are critical to the efficient, cost-effective operation of railroads, so they represent a major focus for automation. A terminal generally contains three types of yards: a receiving yard, where incoming trains from the main line are temporarily stored; the hump yard, where cars are classified and resorted into new trains; and a departure yard, where trains are assembled and stored for dispatch onto the main line.

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.