Railroad Signaling and Traffic Control Definitions

Railroad Operating Rules and Signal Definitions

• Absolute Signal: A fixed signal outside a block system that governs the approach to a block.
• Distant Signal: A fixed signal outside a block system that governs the approach to a block signal.
• Centralized Traffic Control (CTC): A block system that uses block signal indications to authorize train movements.
• Current of Traffic: The movement of trains in one direction on a main track as specified by the rules.
• Controlled Point: A location where absolute signals are controlled by a Control Operator (CO).
• Main Track: A track extending through yards that must not be occupied without authority.
• Controlled Siding: A siding where the signal indication authorizes siding use.
• Station: A place designated by name in the timetable station column.
• Track Bulletin: A notice of conditions affecting train movement.
• Controlled Signal: An absolute signal controlled by a Control Operator (CO).
• Reverse Movement: A movement opposite the authorized direction.
• Track Warrant Control (TWC): A method to authorize train movements or protect men and machines on a main track within specified limits in a territory.
• Electric Switch Lock: An electronically controlled lock that restricts the use of a hand-operated switch or derail.
• Block Signal: A fixed signal at the entrance of a block that governs trains entering and using that block.
• Crossover: A track connection between two adjacent tracks.
• Single Track: A main track where trains are operated in both directions.
• Interlocking, Interlocking Signals, and Interlocking Limits: Signal appliances that are interconnected so that each of their movements follows the other in a proper sequence.
• Absolute Block: A length of track that no train is permitted to enter while the track is occupied by another train.
• Control Operator: An employee assigned to operate CTC or interlocking control machines or grant track permits.
• Signal Aspect: The appearance of a fixed or cab signal.
• Signal Indication: The action required by a signal aspect.
• Special Instructions: Instructions contained in the timetable or other publications.
• Train: One or more engines coupled with or without cars, displaying a marker.
• Trackside Warning Detector: A device that indicates conditions such as Overheated Journal Bearings (hot box), Hot Wheels, Dragging Equipment Detector, or High Water Detector.

Common Railroad Timetable Abbreviations

• A: AI
• R: Restricted Limits
• B: General Orders, notices, and circulars
• T: Turning Facility
• P: Telephone
• Y: Yard Limits
• C: Radio Communication
• J: Junction
• M: Manual Interlocking
• X: Crossover