Hi All, Attached is a pic of the Down Bay starter signal at Maidenhead. The bay is in fact a through platform. In the down direction there are three routes:- Left to the up goods yard and bidirectional goods loop, straight on to the single line branch, and right to the Branch carriage siding. Did the route indicator work just with the main signal arm or also with the smaller calling on arm? In earlier times there had been a three arm bracket signal for the three routes. I assume this had to go due to poor sighting line when the Middle Signal Box beside the up goods loop was replaced by the box shown in my picture. Many thanks for any thoughts? Best regards Paul
Hello Paul, Having studied your picture and from my own knowledge of signalling practice I would say the route indicator and single sub arm formed part of a resignalling scheme making the earlier three arm bracket redundant. The "Down Bay Starter" main arm is what it is a starting signal reading into the forward section or passenger line under the Absolute Block / Token Block arrangements as per Signalling Regulation 4. The subsidiary arm below would not be a "Call On" signal as these normally control movements onto an occupied section which would run onto a terminal bay with stop block and fixed red light, I'd suggest without seeing the signal diagram the sub arm is to signal "Shunt Ahead" non passenger or light engine movements over the three routes. This arm would be electrically interlocked simplifying the mechanical tappet interlocking in the signal box, this then eliminates the requirement for having three levers control shunt moves in which two levers can be dispensed with, the remaining one lever clearing the sub arm instead has electrical interlocking governed by circuit controllers with electric H or U locks which "pick" depending on the route the points are set for. There is also a white diamond track circuit plate attached which suggests the line ahead works under a Line Clear One Pull provision on the main Down Starter signal, the signal plan would show this as an intersecting arrow through the signal on the diagram and a three inch white band painted on the actual lever controlling the Down Starter., there would also be a position route indicator located on the blockshelf for the signalman's aid, this indicator would show either an illuminated A,B or C. on a blue background. Quite simply this was just an upgrading designed to simplify and reduce the mechanical maintenance time of the locking fitter. So to answer your direct question the route indicator box on the signal post denoted to the driver of an engine which of the three routes had been set when the Shunt ahead signal cleared, the post mounted indicator did not govern the main arm which cleared only for the single line section ahead, but it authorized a low speed move to pass the main arm whilst showing a red light effectively cancelling out a S.P.A.D situation.
