A block or interlocking signal without a number plate, or designated by an A marker.
Automatic Block Signal System (ABS)
A series of consecutive blocks governed by block signals, cab signals, or both. The signals are activated by a train or by certain conditions that affect the block use.
A length of track:
• between consecutive block signals.
• between a block signal and the end of block system limits.
• in ATC limits the use of which is governed by cab signals and/or block signals.
A fixed signal at the entrance of a block that governs trains entering and using that block.
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.
A fixed signal outside a block system that governs the approach to a block signal, interlocking signal, or switch point indicator. A distant signal does not indicate conditions that affect track use between the distant signal and block or interlocking signals or between the distant signal and switch point indicator. A distant signal is identified by a D.
Two main tracks where the current of traffic on one track is in a specified direction and in the opposite direction on the other.
General Track Bulletin
A notice containing track bulletin restrictions and other conditions affecting train movement.
Signal appliances that are interconnected so that each of their movements follows the other in a proper sequence. Interlockings may be operated manually or automatically.
A track extending through yards and between stations that must not be occupied without authority or protection.
Track Warrant Control (TWC)
A method to authorize train movements or protect men or machines on a main track within specified limits in a territory designated by the timetable.
Trackside Warning Detector
A device that indicates conditions such as overheated journals, dragging equipment, excess dimensions, shifted loads, high water, or slides.
A system of tracks, other than main tracks and sidings, used for making up trains, storing cars, and other purposes.