Signal mounting of Railway
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 engineer’s or driver’s side of the track.
Gantry mounting
When multiple tracks are involved, or where space does not permit post mounting, other forms are found. In double track territory one may find two signals mounted side by side on a bracket which itself is mounted on a post. The left hand signal then controls the left-hand track, and the right signal the right-hand track. A gantry or signal bridge may also be used. This consists of a platform extending over the tracks; the signals are mounted on this platform over the tracks they control.
Ground mounting
In some situations where there is insufficient room for a post or gantry, signals may be mounted at ground level. Such signals may be physically smaller (termed dwarf signals). Rapid transit systems commonly use nothing but dwarf signals due to the restricted space. In many systems, dwarf signals are only used to display ‘restrictive’ aspects such as low speed or shunt aspects, and do not normally indicate ‘running’ aspects.
Other
Occasionally, a signal may be mounted to a structure such as a retaining wall, bridge abutment, or overhead electrification support.