On 19 October 1987, the Glanrhyd Bridge near Llandeilo in Carmarthenshire collapsed and four people died when a train travelling over the bridge plunged into the River Towy.
The 05:27 service from Swansea to Shrewsbury, had ten people travelling on it, ran onto the bridge over the River Towy at Glanrhyd.
After many hours of heavy rainfall the Towy Valley was flooded, causing the bridge to collapse into the river.
The first carriage of the train fell into the river as it reached the bridge, trapping people inside. Three passengers and three members of British Railways' staff were able to escape.
But Mr and Mrs Evans, 14-year-old Simon Penny and the driver of the train Mr Churchill, drowned.
The bridge was damaged beyond repair and it had to be completely demolished.
Simon Penny's mother said:
In inquest followed to determine how the disaster had happened.
Changes were then introduced to prevent a tragedy like that from ever happening again.
A public inquiry heard that the train should not have been allowed to run and that there were delays in moving passengers to safety.
£900,000 was spent on a new bridge, which was more than a metre taller than the original structure.
Reinforcements were also put in place to protect against flooding.