Electrification of Swansea to London trains 'by 2018'
Network Rail has given its first official dates on when the electrification of most of the lines in south Wales will be completed.
Work on the Great Western main line from London to Swansea will be finished by 2018, but it could up to 2020 to complete the entire south Wales valleys network.
There are also plans to improve signalling in north Wales.
Mark Langman, Network Rail route managing director for Wales, spoke to Felicity Evans on BBC Radio Wales.