At grouping a Great Western steam railmotor took over the erstwhile Cambrian locals to Barmouth across Pont y Bermo. They had been worked conventionally pre-group, partly by one of the three ‘Seaham’ Class 2-4-0Ts or ‘Wrexham tank’ 0-4-4Ts. Lower capacity 48-seat, 59ft railmotors were much used and out-shedded each week at Penmaenpool from Machynlleth. Four cars recorded were Gloucester RC&W-built Diagram ‘Q’ to Swindon drawings. Annual practice saw summer season extensions of some journeys north along the coast line to Dyffryn or Harlech for ‘beach’ trippers. In 1923 an additional excursion platform was built at Barmouth to the south of the level crossing and became the normal departure point for the Dolgelley shuttle. Railmotors were displaced by autos from the summer of 1927. Replacement locomotives were autofitted ‘517’ 0-4-2Ts which in turn gave way to new Collett ‘48XX’ 0-4-2Ts. Summer would see two trailers and the extended journeys up the coast, an evening example as far as Afonwen. In 1923 a loop was installed at Bontnewydd on the ascent east to the summit where the Wnion flowed beside the timber down platform added then. There was an all-wood hipped roof box and a brick main office improved on primitive B&D provision.
Further improvements west of Dolgelley came apace. Barmouth Junction sidings, on the east to south curve of the triangle, were enlarged from just fourteen wagons’ capacity and from one to three roads soon after the GW takeover. Various cheaply constructed wooden bridges, like that at Arthog, were replaced by steel girders. Mawddach shoreline curves were relaid and superelevated so that by 1927 the section to Barmouth Junction was also reclassified as ‘blue’ restriction. The first Churchward Mogul worked through to Barmouth in 1929 when permitted over the estuary crossing by strengthening. Nearly all the‘yellow’ until wartime contingency measures. At Penmaenpool Oswestry had constructed the lowest road toll bridge in 1879 at the ‘Narrows’ with a toll house adjacent to the one-platform station. GW measures here included repairs to the engine shed and bridge. By 1936 the goods loop was upgraded to a full passenger crossing loop and a second basic, wooden platform built. The new signal box was an all-wood hip-roofed version. Uniquely it was the one displayed at the British Empire Exhibition at Wembley in 1924-5 alongside
