Network Rail video
Network Rail and Arriva Trains Wales say the new Loughor Viaduct will carry improved train services to West Wales.
It will carry two tracks between Swansea and Llanelli instead of the previous one.
More top news
Clear skies this evening and overnight will allow for a widespread frost. A cold, crisp and bright start to Friday.
L/Cpl Joshua Leakey, 27, says he is an "average bloke" despite receiving the highest military honour for astonishing bravery in Afghanistan.
Gwent Police has apologised for mistakes made in the way it dealt with the risk Carl Mills posed to the Buckley family.