In itself, Gunnersbury is not a particularly complex area, though there are two possible reversing moves that can be carried out.
The main difference is that the signalling is under Network Rail control and therefore the appearance of some of the signals differs from that which we normally encounter on London Underground.
One allows trains to reverse from the westbound platform back to Turnham Green for the District Line or in the case of Silverlink trains back towards South Acton on the North London Line. As these moves are done in passenger service they are controlled by means of a coloured light 'wrong road' starter. However, the big difference is that, because a driver can be offered two routes, there has to be an indication which rote has been set by the signaller. On London Underground this is usually done by means of a junction route indicator (which either indicates a plain green aspect or a green with three illuminated lights), but at this location it is by a device similar to a 'Theatre Type Route Indicator', which is normally associated with a shunt signal and shows a number. However instead of a number here it shows a letter - 'D' for the District (and therefore back to Turnham Green) or an 'N' for the North London Line.
This move is quite routinely used.
A less frequently used move is from the eastbound platform and which enables a train to go back to Richmond. The big difference here is that, for the District Line, it means that a driver goes onto a part of the North London Line which, for the purpose, has a short extension to our four rail current supply system.
In itself the move is not complicated, but a driver must always take care not to go past the end of the current rails. There are two other unusual factors in this. Firstly the next signal (not shown on the diagram but visible in the photos below) does not have a trainstop associated to it. Secondly there is no 'Limit of Shunt' board to indicate the limit. Our Line Supplement on the subject reads as follows: 'when signal GB8 clears (plain green), proceed at caution, no further than the point where the negative rail ends'. In fact a yellow aspect is also acceptable - this allows the train to proceed as far only as the next signal, which is well within the limit of the 'four rail' layout.
When at the normal stooping point at Gunnersbury, this is the view a driver will expect to see with the Junction Indicator illuminated. Note that on Network Rail there are five white lights, rather than the three found on London Underground for a similar type of signal.
However, if we are to reverse via the North London Line, this is the signal that will clear with either a plain green or yellow aspect.
This picture shows the diverging junction for Turnham Green or North London Line. The points in this case are set towards Turnham Green.
In this picture however the route has been given onto the North London Line and we are now heading towards South Acton. Note the lack of the fourth rail on the adjacent track.
This is the next 'Stop' signal. At about this point the driver is safe to stop the train, secure it fully and to change ends to reverse back into Gunnersbury's westbound platform.
The view from the west end of the train. The Network rail coloured ligght shunt signal is just visible to the left of 'our' line below the centre of the bridge structure.
As the train moves back towards Gunnersbury station (now visible beyond the bridge) the shunt signal is more clearly visible.
This move is done only infrequently. An indication of this is the surface rusting visible on the fourth rail in all the above pictures!