Glossary

This list is meant to help creating a "common understanding" of words used in signalling. the intention is to be explicit but be very neutral in the wording. It is NOT based on US, UK or another specific slang.

The list is not formatted yet... on the TODO list. (use CTRL+F in your browswer for now) The list is ordered in order of defining a word. not Alphabetically.

Section or “track section”: A piece of track that counts as “occupied” if one axle of a vehicle is on that section.

Joint: A point on a track that limits a Section.

Signal: A line side item “transmitting” information to an engineer via a Signal Aspect.

Signal Aspect: Any combination of lights, flashing lights, signs, arms, boards at a signal instructing an engineer to behave a certain way.

Direction Aspect: Any information in an aspect that indicates directly or indirectly a geographical direction. (Directly: feathers like in UK Signalling System. Indirectly: letters/numbers/colours that indicate a diverging route)

Stop Aspect: A Signal Aspect instructing the engineer to stop before the Signal.

Stop signal: A Signal capable of showing a Stop Aspect.

Distant signal: A Signal placed in brake distance from a Stop Signal that cannot show a Stop Aspect.

Repeater signal: A Signal placed between Distant Signal and Stop Signal that cannot show a Stop Aspect

Main Signal: A Stop Signal capable of showing a Proceed Aspect valid for Train Movements only.

Shunt Signal: A Stop Signal capable of showing a Proceed Aspect valid for Shunting Movements only. Note in some countries Shunt Signals are required to show a Proceed Aspect for Train Movements.

Combined Signal: A Stop Signal capable of showing a Proceed Aspect valid for Train Movements or Shunt Movements.

Proceed Aspect: A Signal Aspect allowing the engineer to proceed until the next Stop Signal.

Entrance Signal: A Main or Combined Signal placed on the line allowing the entrance into a Yard.

Exit signal: A Main or Combined Signal placed in a Yard allowing the exit out of a Yard onto the Line.

Start signal: A Stop Signal at the start of a Route.

End signal: A Stop Signal at the end of a Route.

Light Aspect Signal: A Signal showing its Aspects with lights only.

Three Aspect Signalling: Light aspect signals in the United Kingdom that shows the signal aspect sequence green/yellow/red to instruct an engineer to stop at the red signal.

Four Aspect signalling: Light aspect signals in the United Kingdom that shows the signal aspect sequence green/double yellow/yellow/red to instruct an engineer to stop at the red signal.

Approach signalling: A method used in the United Kingdom for instructing a lower speed to an engineer by keeping a stop signal showing a stop aspect until it is assumed that the speed is lowered by the engineer. (Normally done by time interval or detecting train position.)

Interlocking: A method to create dependencies between switches and/or movement directions and a signal showing a proceed aspect.

Route: A series of one or more track sections between two stop signals, or between a stop signal and a buffer end reserved, for exclusive use by a movement before the signal or on the track sections.

Path: A combination of one or more Routes in sequence after each other

Flank protection: A method to prevent that other vehicles can intrude in a route.

Vehicle: A rail vehicle with at least two axles.

Consist: One or more vehicles coupled together.

Turnout: A technical device in a track where vehicles can change from one track to another. (note that the word "switch" or "point" are avoided for programming reasons (reserved words/classes))

Plain Crossing: A technical device in a track where vehicles can cross over to another track.

Crossing: An operational procedure in a yard where two trains pass each other in opposite directions.

Double Slip: A combination of two turnouts and a crossing. In interlocking rules a double slip is treated as a “turnout”. (technically seen it is two turnouts with the backs connected)

Single Slip: A double slip with one connection missing. In interlocking rules a single slip is treated as a “turnout”. Note that depending on the way a vehicle enters a single slip, it is a plain crossing.

Yard: Any place on the track where trains can begin, end, overtake and cross with at least ONE turnout.

Line (or Open Line): The track between yards.

Through Line: The continuation of the line through a yard with Main Tracks.

Main Track: A track in a yard where train movements can take place.

Side Track: All other tracks in a yard then Main Track.

Block: One or more track sections between two stop signals.

Train: A consist with at least one locomotive that is scheduled to move onto the line.

Train Movement: Any movement of a Train.

Shunt Movement: Any other movement of consists other than a Train Movement.

Track Circuit: A technical device that detects occupation of a track section by the short-cutting of an electrical circuit by the axles of a vehicle.

Axle counter: A technical device located at joints, that detects occupation of a track section by comparing the amount of axles going into the track section and going out of the track section. If both counts are equal the track section is clear. (This device can normally be reset by a signaller in cases allowed by operating rules.)