Railroad Signal and Dispatching Terms

ABS: Short for Automatic Block Signal System. A signal system that uses automatic block signals, cab signals, or both to govern a block of rail line.

Approach-lit signal: A railroad signal that only lights when a train is forthcoming which saves on electricity costs and light bulbs.

Automatic block signals: This railroad system allows for automatic control of signals using electric track circuits. By dividing a track into separate sections (called "blocks") which are insulated from each other electrically, and making the blocks part of electric circuits which include line-side signals, a system of automatic train protection is gained. When a train is in a block, it completes the circuit, which then automatically sets the signal behind it (and ahead of it, if the line is signaled for movement in both directions) to red.

Block signal: A line-side signal placed at the beginning of a block that governs the use of that block.

Centralized Traffic Control (CTC): A traffic control railroad system whereby train movements are directed through remote control of switches and signals from a central control panel, enabling trains to pass each other at sidings or interlockings without the need for their crews to stop and throw switches. The trains operate on the authority of signal indications instead of the authority of a timetable or train orders.

Controlled point: A location where railroad switches and/or signals are remotely controlled by a dispatcher.

DTC territory: Short for Direct Traffic Control, it is a segment of line that that is under the control of the railroad dispatcher who authorizes trains to proceed in one or more blocks.

Dwarf signal: A short, ground-level signal that is usually placed trackside.

Home signal: A line-side signal which controls the entrance into an interlocking.

Manual block: A train-control railroad system that is the opposite of automatic block signaling, it is controlled by signals that are either controlled via persons (by whatever means that may be; phone, radio, etc.) or by block-limit signals, or both (again, all controlled and verified by humans, not computers or track circuits).

Searchlight signals: Signals which have only one lamp but can display multiple colors.

Signal indication: The information displayed by a signal (i.e., the particular color[s] showing), which the train crew must read, recognize, and decipher so as to act accordingly.

Track Warrant Control (TWC): A method of traffic control whereby the trains are only capable of operating between to certain points. Known as a track warrant, this form governs and allows a train to operate between these certain points.

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