 By 1980 the bridge 's structure had come under attack from marine woodworm , which threatened its closure . British Rail discovered that woodworm had eaten into 69 of the supporting pillars and estimated it would cost £ 2 @.@ 5 million to repair . Locomotive @-@ hauled trains were banned , which immediately resulted in the loss of traffic from Tywyn , including explosives traffic to and from the factory at Penrhyndeudraeth . That traffic was re @-@ routed via Maentwrog Road railway station and the Conwy Valley Line . However , Gwynedd County Council were opposed to closing the bridge completely as 40 % of all railway traffic in the area was tourist related . The government applied for a £ 2 @.@ 5 million grant from the EEC to repair the bridge , with a further £ 4.6m being spent on improving the signalling . The bridge was closed entirely to traffic for six months during the temporary repair works eventually undertaken , and 30 of the piles were replaced . 
