I've always had an affection for the London & North Western Railway. Francis William Webb not only provided them with their motive power for a long period but was responsible for their signalling. He standardised a series of signal box designs, some of which are still in use (albeit with double glazing units in place of the original horizontal-sliding sashes). He produced two types of rugged mechanical interlocking frame, examples of which also survive. The 'Crewe' power operated system and miniature interlocking frame, with electrically-operated semaphore signals, was also quite successful. However, the vast majority of signals were mechanically operated over wire - and what signals!
They were lower quadrant (where the arm is lowered below the horizontal for 'proceed'), with massive cast spectacles. Webb introduced a corrugated steel arm with a long life. The signal arms were big for good visibility, although there were many situations where restricted space enforced the use of shorter arms. Where there were multiple roads, for instance Fast and Slow, the signals for the less-important line carried a large, white ring. Signal posts were normally wooden.
What particularly distinguished the L&NWR was its predeliction for tall signals - 'sky arms'. During the nineteenth century, the pace of development, both industrial and domestic, introduced much more 'clutter' into the landscape. At night, the number of lights not associated with the railway rapidly multiplied. The L&NWR policy was to ensure that the driver could reliably sight his signals, even against an increasingly 'busy' background. One common technique was to lift the signal arm high above the ground, so that the signal arm (or, at night, the signal lamp) could be readily spotted against the sky. This arrangement was useful, for instance, where an overbridge was situated in front of the signal. The tall signal posts which were needed also required elaborate systems of guy wires to provide sufficient support.
There is a problem as a train approaches, or is detained at, a very tall signal - the signal arm becomes harder to keep in view. Where necessary, 'co-acting arms' were provided near the bottom of the post, operating in concert with the top arm.
At diverging junctions with two possible routes, the L&NWR was quite likely to erect two straight posts side by side, although, where space was limited, it might use a wooden bracket signal or a wooden gantry. The horizontal beam of a wooden gantry would normally be under-stayed with steel rods. Where a number of lines had to be straddled, massive steel structures were produced, usually using Pratt trusses.
When I was young, L&NWR lower quadrants were still fairly common, although the LMS had converted many installations to upper quadrant (where the arm is raised above the horizontal for 'proceed'). At large stations, like Crewe, semaphores had been replaced by colour-light signals, but the Goods Independent Lines at Crewe retained a fair number of the old power-operated semaphores. Some of the miniature interlocking frames survived around Crewe (for example, Crewe Station 'A', Crewe Station 'B', Gresty Lane Number 1).
Chester retained a wonderful selection of L&NWR lower quadrant signals right up until the introduction of a power box by British Rail. I believe some of these were slated for preservation but were cut-up.
The only L&NWR signal I can remember operating myself was the bay platform starter at Dudleyport.
So - what of the 'Bedstead'? This was the nickname for the massive gantry erected south of Rugby station, controlling approaching Down trains. Early in the 20th century, the Great Central Railway was building its line to London. The new line crossed the L&NWR just south of Rugby station on a bridge comprising a series of steel trusses. Because the L&NWR established its route first, the Great Central had to pay for any changes the L&NWR had to put in place. Certainly, the massive new bridge would badly affect the sighting of L&NWR signals approaching Rugby on the down. Since the L&NWR wasn't paying, it designed a fairly lavish replacement signal gantry which achieved fame as 'The Bedstead', featuring arms carried high above the Great Central's bridge, with co-acting arms at a lower level.
There's a lovely comment about the 'Bedstead' in a footplate tale by Professor W. A. Tuplin. A fireman is struggling for steam on a Euston - Liverpool express. Approaching Rugby, he's been told they need "four greens and forty reds". The fireman comments along the lines "I saw the four greens but I didn't have time to count the reds before I was back to shovelling!".
I never saw the Bedstead myself - by the time I was travelling on trains, it had been replaced by multiple-aspect colour light signals with 'line-of-lights' route indicators on simple tubular posts.
For more on L&NWR signalling, refer to the excellent book 'A Pictorial Record of L.N.W.R. Signalling' by Richard D. Foster, published by Oxford Publishing Company in 1982 (SBN: 86093 147 1).