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This poster is inside the shelter on platform 4 at Princes Risborough station. It has the following wording and images:

RISBOROUGH'S RAILWAY STORY

THE PRINCES RISBOROUGH NORTH SIGNAL BOX 1904/5 -present

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Princes Risborough's North Signal Box is the largest of its type and date still standing and was listed in 1988. It was built in 1904/5 as part of the reorganisation of the Princes Risborough's station (see the poster on Risborough's station story) and housed 126 levers which controlled points by means of rods, and signals by means of wires. It is a Great Western Railway 'type 7' design which was introduced in 1897 and continued to be built into the 1920's and formed the basis of the company's signal boxes until the advent of British Railways in 1948. There were around 12,000 or 13,000 signal boxes in Great Britain just prior to the First World War in 1914 but successive economies in working practices reduced numbers from the 1920's onwards. British Railways inherited around 10,000 in 1948 but numbers dwindled rapidly to about 4,000 by 1970. By 2012 there were only around 750 still in use in the country. The points and signals at Princes Risborough have been electronically from Marylebone since 1991 and the box was therefore closed at that date.
Image
The new North Signal Box is shown here c.1905 with the complicated points and signals it controlled. In this early photograph the track is not complete and almost all of the signals are still not yet in use (indicated with a white 'X'). The former Station Hotel can be seen on the left
(photo credit: Leicestershire County Archive)

The North Signal Box consists of two principal elements, stacked one on top of the other. The upper one is a glazed timber superstructure, called the 'Operating Floor' where the levers are housed. The levers operate vertical rods running down to ground level that ultimately operate the points and signals. It also contains the 'block shelf' at eye level above the levers which hold the instruments that allow the signallers to communicate with their colleagues up and down the line. The extent of windows at this level gives the signal box staff an excellent panoramic view of the station and its immediate surroundings. The Operating Floor also contains two fireplaces and a toilet for their comfort.

Below this are two floors in a tall brick substructure known as the 'Locking Room'. The upper part of this houses the interlocking connections that control the movements of the levers and vertical rods. John Saxby first patented a mechanical interlocking system in 1856 to prevent the setting of conflicting points or signals in an unsafe arrangement for trains. A much improved 'tappet locking' technique was patented by James Deakin in 1870 and it is an evolved form of this which can be seen in the box today. Below this, the bottom floor contains the cranks and wheels that transmit the vertical movement of the rods and wires to horizontal to work the points and the signals. These rods and wires run outside through long horizontal slots in the front and back of the box. These slots were progressively bricked-up over the years as the track and signalling was simplified.

Years of minimal maintenance combined with more years of total neglect caused the exterior timbers of the operating floor to suffer from rot and also allowed a weakness in the brickwork below to develop alarmingly. When it was closed in 1991 the box was stripped of many useful items and was boarded up - only the shell and some heavier equipment remained. Volunteers for the Chinnor and Princes Risborough Railway (CPRR) recovered redundant equipment in the station area and for a couple of years were allowed maintenance access to the box, but then this was stopped on grounds of track safety. After several more years of vandalism and weather penetration, the broken windows were boarded-up and the staircase was removed. An inspection in 2011, prompted by a break-in, confirmed the extent of damage. It was feared at this time that the box would become unsafe and would have to be demolished.

Network Rail approved renewed access to the signal box by CPRR volunteers in 2013 and restoration work could be resumed. Rotten timbers have been replaced, the exterior and interior have been painted and metal reinforcements and monitors have been inserted to prevent and assess further structural movement.

Part of the signal box has been brought back into active use by Chinnor Railway's volunteers to control the operation of the CPRR's layout at Princes Risborough.

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Images
i) Signalmen at work in the new North Signal Box
ii) Not to be confused with the North Signal Box! Another early photograph, c.1905, this time of the South Signal Box. This shows clearly the horizontal slot through which the rods and wires emerged to work the signals and points. Immediately behind it is the new goods shed; further back the old station bridge can be seen along with the semi-circular arch of the old goods shed. There is clearly more work still to be done on the new layout (photo credit: Leicestershire County Archive)
iii) The interior of the Signal Box in November 2017 showing continuing restoration work (photo credit: Geoff Huntingford)

Link

Foot of poster
left: This poster has been produced with a grant from Princes Risborough Town Council
right: logo of the Chinnor & Princes Risborough Railway