Transport for Wales Transforming the Core Valley Lines in Wales

Taff's Well depot arial view
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In our pioneering project with Transport for Wales, we took on the monumental task of transforming the Core Valley Lines (CVL) from an ageing network into a contemporary, electrified metro-style service. Acting as an end-to-end infrastructure manager, we’ve designed the innovative solution, we’re developing and delivering it, and then managing the assets.

At a glance

  • Fast, frequent service: Four trains an hour will reduce journey times by up to 20%
  • Innovative engineering: Pioneering a novel ‘discontinuous electrification’ solution in the UK
  • Cost savings: Millions saved in civil works kept the project within budget
  • Net-zero hero: Saving tonnes of carbon, paving the way for sustainable rail
  • Social value: Creating hundreds of new jobs and connecting 1.5 million people

Key metrics

  • £738M


  • 1.5M

    people connected

  • 172km

    of track electrified

From the beginning, this has been more than a transport system; it is a catalyst for transforming the economic and social prospects of South East Wales. The outcome for communities is new, clean, reliable transport from the Welsh valleys into the capital - revitalising the economy, providing sustainable travel and countless opportunities for the people of South Wales.

The brief: More than a transport system

Taff's Well Depot

This project is unusual because the procurement brief was structured around output, underpinned by the legal status of the Future Generations Act in Wales. Rather than a technical specification, the brief was “better access to jobs and services, more frequent and faster services, better quality, and environmental improvements”. As the successful bidder, our challenge was to find the best ways to deliver these outcomes.

Technical challenges and innovations

With free rein over design and delivery, our team was able to consider multiple solutions to electrify the network.

Our primary challenge was designing to meet the needs and challenges of the historic railways of Wales. This task was particularly demanding due to the ageing infrastructure, where historic structures along the route, such as bridges and tunnels, were too low for standard electrification methods. Traditional solutions like demolition or track lowering would be impractical, as they are costly, environmentally damaging, and time-consuming.

Additionally, the presence of listed assets along the route added another layer of complexity, requiring consents for any work on these structures, potentially leading to further delays and complications.

Electric trains in Taffs Well depot
Electric trains in Taff's Well depot
Innovative solution:

Discontinuous electrification

Our solution, 'discontinuous electrification,' reimagined traditional approaches. This method involved:

  1. Permanently Earthed Sections: Introducing non-live overhead cable sections to allow trains to switch to alternative power sources.
  2. Catenary-Free Sections: Routing power cables around obstructions to avoid direct contact with sensitive structures.
  3. Future-proof design: Ensuring that the infrastructure can be easily upgraded if necessary.

Introducing hybrid trains: Advanced Stadler Flirt and City Link trains, with their multi-mode power capabilities (battery, diesel, OCS), can transition through current-free sections, making discontinuous electrification possible.

Results and benefits of discontinuous electrification

Had we not developed our electrification solution, we would have had to demolish and rebuild countless structures, including 50 overline bridges, at a cost of millions, with inevitable environmental impact and a longer, more costly delivery. Key benefits are:

  • Reducing cost and carbon emissions: Eliminating the need for extensive civil engineering works led to significant cost savings and reduced carbon emissions.
  • Streamlined project: Avoiding the challenges of obtaining consents for listed structures streamlined the project.
  • A new model for UK railways: The solution was perfectly suited to the CVL's unique requirements, offering a model for similar projects.

Industry-first innovations

Designing this system required Amey’s engineers to work together to overcome numerous technical challenges. In the process, we’ve delivered many cutting-edge and industry-first innovations, both large and small. Some of these include:

  • Developing an accurate 3D Project Information Model (PIM) to resolve design conflicts, streamline processes, and save time and money through precision.
  • Ensuring the trains met power demands and had adequate battery recharging opportunities. Since the project started, we’ve sourced larger batteries to achieve this.
  • Transferring assets from Network Rail’s management system to ours, a UK first.
  • Addressing high voltage cable and capacity issues through advanced modelling.
  • Collaborating with suppliers to enhance insulator designs for the railway’s needs.
  • Real-time remote track monitors fitted to the passenger trains to monitor assets, reducing typical costs and improving insight.

Inside train depot - Taff's Well

Supporting the local economy

Taff's Well and beyond

Technical innovation aside, the true success of the CVL project is its wide-ranging socio-economic impact. Some of these are hard to quantify, for example many young people can now access educational and career opportunities in Cardiff that would otherwise be impossible. Other outcomes are being realised now.

Taff's Well

A new £100 million depot and Metro Control Centre at Taff’s Well, Rhondda Cynon Taff. has led to significant investment in the local economy. This facility will house the new Metro trains and employ 400 train crew, 35 maintenance staff, and 52 Metro Control Centre staff.

Improving broadband across the valleys

As part of the project, we installed high-capacity fibre cables, bringing fast, resilient broadband to homes, businesses, and organisations along the railway. This is an additional source of income for the network, and thanks to the ability to connect station services like CCTV and ticket machines, it will pay for itself within five years. We expect this innovative business model to be used for future rail telecom projects across the country.

Future economic benefits

Outside of the hundreds of people to be employed in running the metro, improved connectivity is expected to boost employment by up to 7% long term, creating anywhere from 6,000 to 20,000 new jobs.


Setting new standards for sustainable rail

Our work on the CVL represents a significant leap in rail infrastructure modernisation, showcasing how an outcome-led approach can inspire innovative thinking and, in turn, transform local communities.

Blending the deep expertise of our multidisciplinary teams allowed us to navigate the challenges of an ageing infrastructure and set a new standard for future rail electrification projects.

More importantly, our role has gone beyond upgrading infrastructure to creating tangible economic and social benefits for South East Wales, benefits that will still be felt in generations to come.

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