for the Ffestiniog Railway Deviation, the diversionary route built between 1965 and 1978 to bypass the Ffestiniog Power Station pumped-storage hydroelectric power station, one of two pumped-storage schemes in Wales, and its lower reservoir (Llyn Ystradau). The Deviation (this is the conventional name for such railway works) was built mostly by volunteers and involved a long new tunnel constructed by three Cornish tin mining engineers (and some employees) between 1975 and 1977. At the southern end is the spectacular Dduallt spiral formation constructed with its bridge entirely by volunteers to gain an initial height rise of in order (after a further mile of the new railway and the new tunnel) to clear the flooded track bed north of the former tunnel. Parts of the trackless former route can be clearly seen below the new route, particularly just north of Dduallt. The old tunnel is plugged near its northern end, which is usually underwater. Some delicate engineering work was required where the new line passes over the power station pipelines. A pull and push service officially called The Shuttle and powered by diesel locomotive Moel Hebog with carriage 110 was operated from Dduallt to a temporary terminus at Gelliwiog, before the new Moelwyn Tunnel, from 26 May 1975, during two summers, to enable tourists to experience the excellent views from the Deviation route, in advance of the opening of the new Moelwyn Tunnel. For several years before this an earlier Shuttle had run between Tan-y-Bwlch and Dduallt in between the regular trains in the peak period. It was hauled by diesel locomotive Moelwyn with a short train of 4-wheeled coaches. Another temporary terminus known as "Llyn Ystradau" (now dismantled) existed alongside the reservoir during 1977, but passengers were not permitted to leave the station other than by train since it was on Central Electricity Generating Board land without public access. Services References Brian Hollingsworth: Ffestiniog Adventure - The Festiniog Railway's Deviation Project, 1981. Further reading External links The Ffestiniog Railway Company's website Ffestiniog Railway Timetables Multimap Map of Dduallt Heritage railway stations in Gwynedd Ffestiniog Railway Railway stations in Great Britain without road access Maentwrog