A fleet of 36 tram-trains, costing over £200 million in taxpayer funds, remains largely unused more than three years after the first unit was delivered. Transport for Wales (TfW) has stated that the tram-trains, considered the "final piece" of its £2 billion South Wales Metro project, may not be in full service until the end of 2027, significantly later than the originally promised 2022 operational date.
Data obtained by the BBC reveals that fewer than half of the 36 tram-trains have completed the rigorous statutory testing required for operation on the UK rail network. TfW chief executive James Price emphasized the need for trains to function "100% well, 100% of the time" before full deployment.
The South Wales Metro aims to transform an old railway line into a rapid transit system, a project described as Wales' single-largest infrastructure undertaking since devolution. The project has been plagued by delays and cost increases.
Testing and Technical Challenges
Officially designated as Class 398 Citylink multiple units, these trains were ordered from manufacturer Stadler in 2018, with the first arriving in Wales in March 2023. Currently, only six tram-trains are undergoing passenger testing across the valleys network. These units have been temporarily withdrawn at times due to what TfW described as "teething issues" and "early reliability challenges," primarily attributed to software problems.
Twelve of the 36 tram-trains have passed testing, with 20 still requiring the scrutiny mandated by the rail regulator. The testing process, which began in 2024, can take between six weeks and two years per vehicle. Price explained that problems often emerge only when trains are brought into service, citing a significant software issue affecting the entire fleet due to a highly automated system. He noted that improvements can be delivered through software updates rather than extensive engineering changes, which is more cost-effective and efficient.
Stadler confirmed it is "working closely" with TfW to resolve "minor issues" with the "battery tram-trains," stating that testing and validation have involved normal refinements, including software updates.
Delays and Infrastructure
Part of the delay is attributed to the completion of line electrification infrastructure, which was only finished in March due to disruptions from the COVID-19 pandemic and supply chain impacts from the war in Ukraine. TfW stated that they saved approximately £400 million and years of time by using on-board batteries for sections without overhead electrification, rather than electrifying the entire 105-mile network.
However, some experts express concern that the tram-trains are too complex for the project's goals. Rail engineer Gareth Dennis suggested that the ambition to reduce infrastructure costs by using highly complex trains requires numerous systems to function correctly and reliably, which presents significant testing challenges.
TfW noted that similar technology is already operational on their larger Class 756 trains, which are serving as a temporary solution. The introduction of the tram-trains is considered the "final piece" of the South Wales Metro, with full service on three lines between Cardiff and Aberdare, Merthyr Tydfil, and Treherbert anticipated by the end of 2027. This includes the rollout of four trains per hour, a target initially set for 2022.
Opposition politicians have criticized the situation, with Reform's shadow transport minister Jason O'Connell stating that taxpayers "deserve to know what has gone wrong, how delays have turned into years and the costs are spiralling out of control."
The Welsh government acknowledged that while some issues have delayed the tram-trains' introduction, TfW remains on track to complete the full rollout by the end of the coming year, having already delivered "transformative improvements" to the valleys network.