Future of Rail | £1bn Core Valley Lines upgrade to help drive modal shift in Wales

Upgrades underway on South Wales’ Core Valley Lines will improve capacity and deliver decarbonisation.

Switching people’s travel preference from car use to public transport and active travel is key to achieving net zero, according to Transport for Wales (TfW).

TfW chief executive James Price highlights the need to switch in the organisation’s latest corporate strategy.

And TfW is already delivering new schemes to do just that with the South Wales Metro project a key example.

A vital part of the South Wales Metro project is the transformation of the Core Valley lines so they can provide more frequent and faster services for passengers.

This network currently has 180km of track and 52 stations serving the rural communities of the South Wales Valleys. It was transferred from Network Rail to Transport for Wales in March 2020.

Large sections of the Core Valley lines between Cardiff and Aberdare, Coryton, Merthyr Tydfil, Rhymney and Treherbert are single track, while some of the equipment used dates back to the early 1940s.

The project’s aim is to upgrade the infrastructure and technology of these lines to accommodate new, faster electric trains and to enable the introduction of additional services.

The Welsh Government, the UK Government and the European Union’s EU Regional Development Fund allocated an initial £738M to the project in 2018.

Covid and inflation have eaten into this and the funding partners have had to add £306.7M to the pot to deliver the work. The extra funding was secured in November 2022.

Craidd Alliance, a consortium of Transport for Wales (TfW), Alun Griffiths, Amey Infrastructure Wales, Balfour Beatty Rail and Siemens Mobility is delivering the project.

Track changes

The project involves laying 180km of new track, partly to convert 11 sections to twin track line and the rest to create 11 new passing loops.

It also includes electrification of 170km of track to power the new fleet of fully electric Class 398 tram-trains which will be introduced to the network. The overhead line electrification will require the installation of close to 3,500 piled foundations, 3,000 masts, 9,000 cantilevers – fixed to the masts and hold the overhead cable – and 675 cable runs.

Work will also be carried out at all 52 stations across the network.

Platforms will be extended to accommodate the higher capacity trains, while new ones are to be constructed at stations on the sections converted to twin track.

The way I look at these programmes is the legacy of what we leave behind

There are also plans to build new stations at Crwys Road on the Rhymney line and Butetown on the Cardiff Bay line – the 1.7km line connecting Cardiff Bay station to Cardiff Queen Street – as well as to relocate Treforest Estate station on the Merthyr Tydfil line.

A new £100M tram-trains depot is also being constructed at Taff’s Wells. The depot will be the control centre for the Treherbert, Aberdare and Merthyr Tydfil railway lines.


Work started on site in summer 2020 and TfW initially aimed for the project to be completed by the end of this year. But Covid-19 related delays and unexpected issues with utility diversions have meant that it is now estimated to be completed towards the end of 2024.

In some areas a smart electrification system which enables trains to switch between mains and battery power is eliminating the need for full scale electrificaton.

“We are working among an exceptionally densely populated urban area in and around various communities, by using this smart technology we avoid rebuilding around 50 structures,” says TfW rail infrastructure director Karl Gilmore.

A milestone for the electrification work was celebrated in May with the completion of the £77M signalling and electrification for the first section of track between Cardiff and Pontypridd. This covers the line between Cardiff and Radyr which links to several other Core Valley lines.

The project team has also started laying the new track, following the completion of utility diversions, across all the lines.

While the work has caused disruption to local communities, the project’s backers believe that when the new infrastructure is built, local residents will recognise its benefits.

“Quite often people get focused on what we’re building, rather than the benefits to the community.

“The way I look at these programmes is the legacy of what we leave behind,” says Amey rail director Wayne Brigden.

Gilmore agrees and emphasises that the improved connectivity between communities could regenerate the older industrial areas around the Core Valley lines. 


Modernising theTreherbert Line

The 37.5km Treherbert line, also known as the Rhondda line, currently runs one train an hour between Cardiff and Treherbert, a small village in the county borough of Rhondda Cynon Taf.

The line operates on single track from Treherbert to Porth with a passing loop at Ystrad and then twin track from Porth to Cardiff. To enable trains to pass each other and increase service frequency to four trains per hour, sections of the single track will be upgraded to double track. In addition, three new passing loops will be constructed, supported by six switch and crossing installations.

For the planned train frequency to be achieved, the line’s old Token Exchange Signalling System must be replaced with a modern signalling system. The Token Exchange equipment, dating back to the 19th century, involves the use of a key that is collected by the train driver and then inserted into a token machine at different points along the line to send a signal to the signaller.

Contractors working to transform the line are currently in the middle of an eight month blockade that began at the end of April.

“The interventions are measured in hours, not in in weeks because we have to operate at that level of detail. The scheduling and integration of the work is paramount to the success of the project,” says Balfour Beatty Core Valley lines project manager Alasdair MacDonald.

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