Signals on Londn Transport

pigs ear signal

Open Section Signal Head.
The 'Pigs Ear' is just visible as the small red light just to the left of the main signal aspect.

Rail Gap indicators are sometimes attached to signals These are traction current rail gaps and are marked by special signals which only illuminate when the current is off in the section ahead. "Rail Gap Indicators consist of three red lights in a white triangular plate marked as such. Their repeaters are similar but both lights and plates are yellow.

LT signal

A complicated looking signal?
Actually it's not really. The top two aspects are the important ones - automatic signal 909a which shows red or green. In this case it's green - but if it was red, the train would have to stop here.

The next two aspects (green or yellow) are repeaters for the next two signals (A909b & A909c).

The bottom two with the white background are known as a fog repeater, in this case, also for A909b & A909c. Fog repeaters are intended to add extra warnings in bad weather, but are now used all year round to mitigate against SPADs.

signal with junction indicator

Semi-Automatic Signal with Junction Indicator illuminated.

In this example the signal is located at Hanger Lane Junction. The signal indicates that the route has been set towards Ealing Broadway. If the Signal showed only a green aspect the route would have been set towards North Ealing. WM20/21

Route indicators are the familiar line of white lights at junctions, Junction Route Indicators known as Harbour Lights. For shunting moves to two or more routes a matrix of individual lamps called a Theatre Route Indicator is used. When a move is set up "1" is used for the leftmost route, "2" for the second from left and so on.

The dual red/green aspect is caused by the associated trainstop arm being slow to drop when the signal goes to green. The section ahead being clear allows the proceed aspect to illuminate but the red stays lit until the trainstop is proved to be fully down.

Shunt Signals [below]
Shunting and subsidiary signals are white discs 15" inches in diameter and externally illuminated. Shunt signals have a horizontal red band rotate 45 degrees anti-clockwise to show "proceed". Where subsidiary signals are still in use they are again white but with two red lines across the middles and carry either "W" for a Warning Signal or "C" for a Calling On Signal. Subsidiaries are used when a second train is to enter an already occupied platform.

calling on signal

Calling On Signal - now redundant.
This example is located on the eastbound approach to Parsons Green. WF37

shunt with Rout indicator

Shunt Signal at Danger, with Theatre-type Route Indicator above.
When When the signal is cleared the Route Indicator would illuminate showing the route number set. WM7