Most South Wales Metro tram-trains still await testing as rollout slips to 2027

Sixteen of Transport for Wales’ 36 new tram-trains have passed statutory testing, while the rest remain under scrutiny more than three years after the first vehicle arrived in Wales. The operator now expects the fleet to enter full service by the end of 2027, five years later than originally promised.

The trains, built by Swiss manufacturer Stadler, cost more than £200m in total. Six are currently being tested with passengers on routes in the South Wales Valleys, but they have occasionally been withdrawn because of software problems and what TfW calls early reliability issues.

TfW chief executive James Price said the operator wanted the trains to work reliably before a wider rollout. He described the delays as frustrating but said they were not unexpected, adding that software was the fleet’s biggest issue. Stadler said it was working with TfW to address what it described as minor issues and make software updates during testing.

The Class 398 vehicles are designed to operate both on urban streets and on railway lines. Their introduction is part of the South Wales Metro project, which aims to increase services between Cardiff and Aberdare, Merthyr Tydfil and Treherbert from two trains an hour to four. TfW says that increase is expected by the end of 2027.

The company says delayed completion of electrification infrastructure, including disruption from Covid and supply-chain effects linked to the war in Ukraine, contributed to the timetable slipping. It also says staff training and signalling work at Cardiff Queen Street station are needed before the full service can begin.

Rail engineer Gareth Dennis said combining tram and train functions, batteries and sections without overhead wires made the project unusually complex and increased the testing required. TfW says using batteries on non-electrified sections saved about £400m and years of work compared with electrifying the whole route.

The operator says the fleet is central to delivering faster, more frequent services across the network. Until the tram-trains are ready, Class 756 trains are operating on the Valleys routes; TfW says those trains will eventually move to the Bridgend–Rhymney line.