Pencader Tunnel
Pencader Tunnel is an abandoned railway tunnel on the old trackbed of the Carmarthen to Aberystwyth main line in south-west Wales. It was originally bored for the Llanpumsaint-Pencader section of the Carmarthen & Cardigan (C&C) Railway.
It is approximately 985 yards (901 m) long (just over half-a-mile), making it the longest tunnel in West Wales and is bored through Ordovician shales. It is single-track and built to the C&C's adopted broad gauge dimensions, as opposed to the smaller standard gauge used on Britain's railways today. It is also known as alternatively Alltwalis Tunnel and Dolgran Tunnel to local villagers.
From the first proposals of the Carmarthen and Cardigan railway it was known that an expensive and long tunnel would be needed to take the line between the valleys of Skanda Vale and Dolgran, under the Brechfa Forest watershed. Several separate Engineers surveyed the line, including Isambard Kingdom Brunel, with varying schemes. Brunel proposed a dead-straight tunnel to connect the valleys, though after reworking, the final design was longer in order to ease the gradients.
As built, the tunnel was approximately 985 yards (901 m) long, curving slightly from the southern portal in Skanda Vale, running straight for most of its length and then curving for the final third into Dolgran. The digging would require two construction shafts which could then be used for ventilation. Construction started in the spring of 1857 to bore the tunnel at the same time as work began on the first stage of the railway line in the town of Carmarthen.
During construction in 1859, the C&C railway attempted to switch from broad gauge to standard gauge, which would have meant all railway infrastructure (including the tunnel), could be built to smaller (and thus cheaper) dimensions. Such a change would require the approval of the British Parliament and pressurisation on the company by the South Wales Railway, a broad gauge line in the area which did not want the rival standard gauge making an incursion on its territory, meant the application to Parliament never occurred.
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