 The bridge crosses the estuary of the River Mawddach from Morfa Mawddach near <unk> northwards to the edge of Barmouth . The line is operated by Arriva Trains Wales , with connecting services south to Aberystwyth and east to Welshpool and Shrewsbury . The section containing the bridge is on the Cambrian Coast railway between Machynlleth and Pwllheli . The bridge is a Grade II * listed structure about 699 metres ( 764 yd ) long and contains 113 wooded trestles supported by a series of cast iron piers . It is one of the longest timber viaducts still standing in Britain . 
