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Southern Signals
Colour Light Signals

Shunt signals

As was explained in the introduction, a colour light shunt signal is referred to as a position light signal and only gives a driver permission to proceed as far as he can see the line is clear. It does not tell him whether or not the road is clear to the next signal (if there is one), so he has to be prepared to stop at any moment. This is necessary as otherwise no movement could be made onto a line that is already occupied. Just a couple of examples are where entry is required to sidings which have stock already in them or a loco moving on shed with another loco already occupying the approach road. Such signals will be "red" ones, where the proceed aspect is shown by two white lights at an angle of 45° and the stop aspect by horizontal red and white lights, or on the latest versions, two horizontal red lights. Where a position light signal is associated with a main running signal then it can only ever show the proceed aspect. One such signal is the calling-on signal (where an engine sets back onto the coaching stock) which, being located under a running signal head, will have two aspects that show white lights at an angle of 45°, with the main signal head showing a red aspect, for proceed with caution, and no lights at all otherwise as the main signal head shows the necessary aspect.

Such signals will also control movements over a crossover and into and out of sidings. Once inside the sidings, however, there is frequently no need for further signals. Sometimes a sidings exit signal will be placed where it can only apply to the exit road, so will be a red PLS, and sometimes where it could also be taken to apply to one or more other roads. In this latter case the PLS will be a "yellow" one that displays two white lights at 45° for proceed in the direction to which the signal applies, or a horizontal yellow and white light for stop, with movements allowed in the direction(s) for which the signal cannot be cleared, with the latest signals exhibiting two horizontal yellow lights in place of one yellow and one white. For both the yellow and white or the two yellow aspects the meaning is that the signal may be passed when "on" provided the movement is not in the direction to which the signal applies, i.e. not exiting the sidings.

This photograph is of signal DH6 at East Dean, between Salisbury and Romsey. Taken in December 1999, the signal and ground frame controlled access to and from a quarry siding which, by this time, was long disused. The image on the right has been digitally altered to suit our purpose!

Left: The signal showing the usual stop aspect. The red light in the main head means there is no need to show a red aspect on the subsidiary position light signal.

Right: Now the main signal head shows a stop aspect but the subsidiary position light signal shows a proceed aspect, allowing a driver to pass the signal but also telling him he must proceed with caution as the line ahead may be occupied and that he must be prepared to stop short of any obstruction.

photograph: Mike Morant collection

Signal	Meaning
	Stop
	Stop
	Stop.	Applies only to movements in the direction(s) to which the signal can be cleared. Other movements can pass the signal without it being cleared.
	Stop.
	Obey the main aspect. (Associated with a running signal).
	The line ahead may be occupied. Proceed cautiously towards the next stop signal or buffer stops and be prepared to stop short of any obstruction.
	As above but used in association with a running signal.
	Stop. The equivalent of the old 'Limit of Shunt' board.
In addition, where associated with a main running signal and controlling the entrance to either a goods loop or a siding, a single yellow light may be displayed under the red running signal which has the same meaning as two white lights.


photograph by Glen Woods	photographs by Peter Richards		photograph by Edmund Copping
A modern PLS at Brighton showing to good effect the double red aspect.	The older version showing red and white aspects, with the same meaning as two reds, from when the technology for changing the aspect from white to red had not been introduced.	The off position. This will be the same for each type of position light signal shown on the left. Under wraps is a Westinghouse disc.	A yellow PLS photographed at Fratton Depot on 28th December 2003. Many position light signals now have their number displayed underneath the aspects, together with an arrow pointing to the line to which they apply.

Many position light signals now have their number displayed underneath the aspects, together with an arrow pointing to the line to which they apply.

Southern Signals Colour Light Signals

Shunt signals

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Southern Signals
Colour Light Signals