Railway signal


Not to be confused with the signals along roadways at level crossings.

This article is about physical railway signal devices. For the principle of railway signalling, see railway signalling.



Colour light (British)



Two common types of signal. In both cases, the left signal shows “danger”.

A signal is a mechanical or electrical device erected beside a railway line to pass information relating to the state of the line ahead to train/engine drivers (engineers in the US). The driver interprets the signal’s indication and acts accordingly. Typically, a signal might inform the driver of the speed at which the train may safely proceed or it may instruct the driver to stop.


  • 1 Application and positioning of signals
  • 2 Aspects and indications
  • 3 Signal forms
    • 3.1 Mechanical signals
    • 3.2 Colour light signals
    • 3.3 Position light signals
    • 3.4 Colour-position signals
  • 4 Signal mounting
    • 4.1 Post mounting
    • 4.2 Gantry mounting
    • 4.3 Ground mounting
    • 4.4 Other
    • 4.5 Filaments
    • 4.6 Lamp proving
  • 5 Control and operation of signals
  • 6 Cab signalling
  • 7 Signalling power
  • 8 See also
  • 9 References
  • 10 Notes
  • 11 External links

Application and positioning of signals

Main article: Application of railway signals



Aspects and indications


Signal forms

Signals differ both in the manner in which they display aspects and in the manner in which they are mounted with respect to the track.

Mechanical signals

Main article: Railway semaphore signal


Radio Electronic Token Block or RETB).

Colour light signals



Position light signals


PRR position light signal

Colour-position signals


Signal mounting

Lineside signals need to be mounted in proximity to the track which they control.


Post mounting

When a single track is involved, the signal is normally mounted on a post which displays the arm or signal head at some height above the track, in order to allow it to be seen at a distance. The signal is normally put on the engine driver’s side of the track.

Gantry mounting


Ground mounting


Signalling power