Regular use of this facility probably ceased about 1872 with the opening of Tan-y-Bwlch station (although up goods trains are said to have been required to stop at Dduallt for examination prior to passing through Moelwyn tunnel).

The present buildings at Dduallt are a water supply tank (now out of use), a stone built shelter constructed by volunteers in 1998, and Rhoslyn cottage, which latterly was always privately owned until it was bought, derelict, by the Festiniog Railway Company in 2005.

The Deviation (this is the conventional name for such railway works) was built mostly by volunteers and involved a 310 yards (280 m) long new tunnel constructed by three Cornish tin mining engineers (and some employees) between 1975 and 1977.

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.

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.