The UK Government has confirmed plans to electrify the line from Cardiff to Swansea, as part of a UK-wide £9bn investment in the rail network.
The Ebbw Vale, Maesteg, Merthyr Tydfil and the Vale of Glamorgan lines will also be electrified.
The project, which will cost more than £600m, to be spend during the period 2014-2019.
This investment sends out a clear message that Wales is open for business. Electrifying the rail line to Wales’ second city and to the South Wales Valleys will give people in these areas a chance to fulfil their potential by improving connectivity to labour markets and opening up prospects for jobs and investment.
The UK Government announces plans to electrify the line from Cardiff to Swansea, as well as several Valleys lines
There are reports that UK Transport Minister will announce a £1bn project to electrify the railway lines in south Wales.
Theresa Villiers will visit the Welsh Assembly to discuss rail electrification for Wales, but isn't expected to announce further plans.