[5][4] After the Welsh Government, supported by parties including a CBP team led by Mark Barry, lobbied at Westminster for the extension of the Great Western Main Line electrification programme west to Swansea, and north into the South Wales Valleys, Barry developed a more detailed blueprint plan for Cardiff.

They produced a further interim report, "A Cardiff City Region Metro: transform | regenerate | connect" published in February 2013.

[9] She also set up a working group to examine detailed proposals for the potential subsequent stages of the Cardiff Capital Region Metro system.

[17] In August 2019, it was announced that work on the project would be delayed due to "unresolved issues", particularly around maintenance cost estimates,[18] which are preventing sale of the freehold land, buildings, and operational assets, by current owner Network Rail to the Welsh Ministers.

[18] The deal would require approval from the Office of Rail & Road before contractor KeolisAmey Wales could undertake work including electrification and other improvements.

[18] It was announced that work on the project would start on 3 August 2020, beginning with track improvements on lines to Merthyr Tydfil, Aberdare and Treherbert.

[19] Total cost of South Wales metro part 1 has been cited by the Welsh government as £88.5 million in a brochure on the development.

[20] The total cost of South Wales Metro part 2 is estimated to be £738 million; this includes "electrification of the CVL; double tracking of selected route sections; a direct connection from the Treherbert, Aberdare and Merthyr Tydfil lines to Cardiff Bay; and a new train stabling facility at Taff’s Well".