The following definitions are taken from the “General Code of Operating Rules”, effective April 28, 1985. And yes I know that the GCOR came into effect at two different dates depending on the railroad. I am using the date it first came into use.

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Absolute Block

A length of track in which no train or engine is permitted to enter while it is occupied by another train or engine.

Absolute Permissive Block (APB)

A designated section of track or tracks within which the movement of trains will be governed by block signals, whose indications supersede the superiority of trains. The block signals may be controlled manually or automatically.

Absolute Signal

A block or interlocking (signal box) designated by an “A” marker or the absence of a number plate.

Automatic Block Signal System (ABS)

A series of consecutive blocks governed by block signals, cab signals or both, actuated by a train, engine or by certain conditions affecting the use of the block.

Automatic Cab Signal System (ACS)

A system which provides for the automatic operation of the cab signals and cab warning whistle.

Automatic Train Stop System (ATS)

A system actuated by wayside inductors, so arranged that its operation will automatically result in the operation of the brakes until the train has been brought to a stop.

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A length of track between consecutive block signals or from a block signal to the end of block system limits, governed by block signals, cab signals or both.

Block Occupancy Indicator

An indicator used to convey information regarding block occupancy.

Block Signal (Home signal)

A fixed signal at the entrance of a block to govern trains and engines entering and using that block.

Block System

A block or series of consecutive blocks within APB, ABS, ACS, CTC or interlocking limits.

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Cab Signal

A signal located in engineer’s (driver’s) compartment or cab, indicating a condition affecting the movement of a train or engine and used in conjunction with interlocking signals and in conjunction with or in lieu of block signals.

Centralised Traffic Control (CTC)

A remotely controlled block signal system under which train movements are authorised by block signals whose indications supersede the superiority of trains.

Controlled Siding

A siding within CTC or interlocking limits, the authorisation for use of which is governed by signal indication or control operator.

Controlled Signal

An absolute signal, the aspect of which, is controlled by a tower (signal box) operator (signaller).


A track connection between tow adjacent tracks.

Current of Traffic

The movement of trains on a main track, in one direction, specified by the rules.

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Distant Signal

A fixed signal outside of a block system, used to govern the approach to a block signal, interlocking signal or switch point indicator. It will not convey information as to conditions affecting the use of the track between the distant signal and block signal (Home Signal), interlocking signal or switch point indicator to which the approach is governed. It will be identified by a “D” marker.


A portion of the railroad designated by timetable.

Double Track (DT)

Two main tracks, on one of which the current of traffic is in a specified direction, and on the other in the opposite direction.

Dual Control Switch

A power-operated switch, also equipped for hand operation.

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Electric Switch Lock

An electrically controlled lock device affixed to a hand operated switch or derail to control its use.


A unit propelled by any form of energy, or a combination of such units operated from a single control, used in train or yard service.

Extra Train

A train not authorised by timetable schedule. It may be designated:

  • Extra: For any extra train except work extra, the movement of which is authorised in a specific direction.
  • Work Extra: For an extra train authorised by Form H train order, the movement of which may be within either direction within specified limits.

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Fixed Signal

A signal of fixed location indicating a condition affecting the movement of a train.

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Initial or Original Station

The first station on each subdivision from which a train is authorised to occupy the main track.

Interlocking (Signal Box)

An arrangement of signal appliances so interconnected that their movements must succeed each other in proper sequence. It may be operated manually or automatically.

Interlocking Limits

The tracks between the outer opposing absolute signals of an interlocking.

Interlocking Signals

The fixed signals of an interlocking, governing trains using interlocking limits.

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Main Track

A track extending through yards and between stations which must not be occupied without authority or protection.

Multiple Main Tracks

Two or more main tracks, the use of which is designated in the timetable.

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Overlap Sign

A sign marking the limit of control of a block signal.

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An employee assigned to a train when the engineer or conductor is not acquainted with the rules or portion of railroad over which the train is to be moved.

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Register Station

A station at which a train register is located.

Regular Train

A train authorised by timetable schedule.

Restricted Speed

A speed that will permit stopping within one half the range of vision; short of train, engine, railroad car, stop signal, derail or switch not properly lined, looking out for broken rail, not exceeding 20 MPH.

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That part of a timetable which prescribes class, direction, number and movement for a regular train.


A track auxiliary to the main track for meeting or passing trains. The timetable will indicate stations at which sidings are located.

Signal Aspect

The appearance of a fixed signal conveying an indication as viewed from the direction of an approaching train; or the appearance of a cab signal conveying an indication as viewed by an observer in the cab.

Signal Indication

The information conveyed by the signal aspect.

Single Track

A main track upon which trains operate in both directions.

Spring Switch

A switch equipped with a spring mechanism to restore the switch points to original position after having been trailed through.


A place designated in the timetable station column by name.


A portion of a division designated by timetable.

Superior Train

A train having precedence over another train.

Switch Point Indicator

A light type indicator used in connection with facing point movement over certain switches to indicate points fit properly.

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Terminating Station

The last station on each subdivision to which a train is authorised to occupy the main track.


The authority for the movement of trains subject to the rules. It may contain classified schedules and includes special instructions.

Track Bulleting

A notice containing information as to track conditions or other conditions, necessary for the safe operation of trains or engines.

Track Permit

A form used to authorise occupancy of main track where designated by special instructions.

Track Side Warning Detector

Wayside detectors which are provided at various locations as shown in the timetable which detect such conditions as overheated journals (hot boxes), dragging equipment, excess dimensions, shifted loads, high water and (rock or earth) slides.

Track Warrant Control (TWC)

A method of authorising movements of trains or engines or protecting men or machines on a main track within specified limits in territory designated by special instructions or general order.


An engine, or more than one engine coupled, with or without cars, displaying a marker and authorised to operate on a main track.

Train Register

A book of forms used at designated stations for registering time of arrival and departure of trains, and such other information as may be prescribed.

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Variable Switch

A switch, designated by letter “V” or bowl painted yellow, when trailed through the switch points remain lined in the position to which forced.

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A system of tracks, other than main tracks and sidings, used for making up trains, storing of cars and for other purposes.

Yard Limits

A portion of the main track, designated by yard limit signs and timetable, train order Form T, or track bulletin, which trains and engines may use as prescribed by Rule 93.

Yard Engine

An engine assigned to yard service.

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A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z


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