The Future - Signalling Princes Risborough North Signal Box
At present our heritage trains run in and out of Princes Risborough over the Network Rail siding between Thame Junction and the outskirts of Princes Risborough (see picture alongside) under a Track Access Contract and an agreed ‘Method of Working’ (MoW). That present day siding was once the single line that went via Thame to Oxford. Decaying alongside it and covered in undergrowth is the disused Watlington branch track. Planning has started to restore this track so that the Chinnor & Princes Risborough Railway can use it as an independent line removing the need for a complicated and at times, restrictive sharing of the siding. With the introduction of the Chinnor Independent Line will come the need to expand the signalling and pointwork controlled by our signal box. Additional cranks and pulleys have already been installed to carry the point rodding and signal wires, whilst levers and interlocking are being prepared in the South end of the signal box. The first signal post has been erected at the exit of Risborough Platform 4 and more posts are already in the restore-repaint-replant production line. These will be needed to signal trains when the pointwork to change tracks onto the Chinnor Independent Line is installed. They won’t be fitted with signal arms until the whole system is ready to be commissioned, hopefully by 2023. On the sub floor beneath the signal levers is a mechanical interlocking frame, shown below. This frame is basically a mechanical computer, invented decades before the first electronic computers, that prevented the signalman from accidentally setting signals and points that would lead to conflicting train paths and potential collisions or derailments. As mentioned previously, the signal box operating level has been partitioned, splitting the box into two separate areas, north and south. The operating area will be in the south end, nearest to the platform, whilst the north end of the box is anticipated to be a demonstration area of railway signalling and operating practices. There will be separate interlocking frames under each section. With the addition of new signals and points, we had to redesign the interlocking to ensure the necessary protections were put back in place so the safety of our passengers and trains is assured. We have so far completed the mechanical part in the south end but we will be adding electrical controls and indicators for additional safety. For those who would like further reading on railway signalling in general, here are a couple of good websites that will provide more information: https://en.wikipedia.org/wiki/Railway_signalling and https://www.signalbox.org
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NR Thame Branch Siding
Chinnor Independent Line