PHOTO GALLERY: NORTH BRITISH RAILWAY
Swing Bridge East
OPENED: 1899 CLOSED: 1997
Click or tap the images for enlarged views
A swing bridge was necessary where the North British Railway’s Polmont to Larbert line crossed the Forth & Clyde Canal, and the associated signalling was extraordinarily complex.
The line had been single until 1899, but with the doubling, a new bridge and two new signal boxes were necessary.
This rather interesting picture actually shows three signal boxes, if you study it closely! In the foreground is Swing Bridge East (no location-identifying prefix to the name was deemed necessary here) and beyond the level crossing, swing bridge and another level crossing Swing Bridge West can be seen. In the far distance is the rather larger Swing Bridge Junction signal box which controlled a freight branch junction.
East and West boxes changed status in 1908 – until then Swing Bridge East was not a block post, being worked as a ground frame under the supervision of Swing Bridge West. But in 1908, the signalling instruments were moved to Swing Bridge East and the West box became the “ground frame”, solely controlling the level crossing that side of the canal.
The following plans may assist with understanding the changes:
Things changed again in 1927, when Swing Bridge West was abolished, and the control of its level crossing transferred to Swing Bridge East, using electrically powered gates. The signal box was not demolished for many years, though, as can be seen in the 1961 photograph above.
The bridge was worked by hydraulic power from the building behind Swing Bridge East and one wonders about the purpose of the tall tower – did the signalman have to climb up there each time the bridge needed opening? It isn’t as if this is a huge waterway, it is just a small canal.
This view inside Swing Bridge East shows the 19-lever frame built by Stevens & Sons at their Glasgow works. It was numbered from 0 to 18; lever 0 had been added in 1908. The lever numbered “20” in the foreground is actually part of an additional two levers in a “subsidiary frame”, illustrated below. As at Banavie Swing Bridge, Sykes & Co Lock & Block instruments provide additional protection against the acceptance of trains and the risk of their “going in the drink” while the bridge is open. A large indicator at the right-hand end of the instrument shelf (with a badly peeling painted face) shows the position of the bridge and its associated facilities.
Looking closely at the Sykes & Co instruments, the top indicators on the left two instruments, plus the two on the right, show them to actually be three-position Sykes instruments. They have no switch-hook as normally provided, but instead have a “normal-looking” commutator provided at the foot of the instrument. They also have no key-release facility, which was a standard feature (or, rather, non-feature!) on Lock & Block instruments on the NBR.
The centre instrument is rather different and is for the signal leading into the goods loop and the treadle that back-locks it.
This picture shows the “subsidiary” frame of two levers mentioned above, making the total levers up to 21. This is of the Stevens & Sons Dwarf type, designed for ground frames but often used elsewhere. These two levers worked the “Raising Lever” and the “Turning Lever” but it is doubtful the bridge could be raised (it is always necessary to lift a bridge slightly to be free to turn!) or actually turn it directly by levers and this function was probably carried out from within the large building behind the box with these levers merely providing the interlocking between the lever frame and the hydraulic apparatus.
Two gate wheels are provided, it isn’t really clear why but the West box also had two wheels for its level crossing.
The entrance to a goods loop was also controlled from here. All in all this signalman had a lot of responsibilities!
This more recent picture shows the interesting three-penny bit window arrangement at the bridge end of the signal box – provided to give the best possible view of the swing bridge and the two level crossings.
The canal was de-commissioned in December 1962 and both the tow-path level crossing and the bridge were subsequently de-commissioned. Canal Road crossing was busy enough to justify later replacement by a bridge (it is the A9) so in its last years the box had lost much of its importance. In 2001 the canal re-opened. The bridge remains in situ but it is not movable – the rails are now continuous across it.
The signal box continued in use through to re-signalling in 1997, when Track Circuit Block was introduced along the line, controlled from a small cabin at Polmont Junction.