£200m Welsh tram-trains sit mostly unused three years after delivery, with full service now pushed to 2027

Six tram-trains are currently carrying passengers on the south Wales valleys network, in a testing phase, and that is most of what a fleet of 36 has to show for more than three years since the first unit arrived. The vehicles, which cost more than £200m of public money, were originally due to be fully up and running by 2022. Transport for Wales chief executive James Price now says full service might not come until the end of 2027.

The tram-trains are what TfW calls the final piece of its £2bn South Wales Metro, the plan to turn an old Victorian railway into a turn-up-and-go rapid transit service in the mould of the London Underground or Manchester Metrolink. It is the biggest single infrastructure project in Wales since devolution in 1999, and it has been hit by delays and rising costs. The Welsh government-owned operator has missed a number of its own targets for bringing the vehicles into service.

Officially Class 398 Citylink units, they were ordered from the Swiss manufacturer Stadler in 2018, and the first reached Wales in March 2023. The King and former Prime Minister Keir Starmer have ridden one; barely any passengers have. Each unit is worth about £8m and can run on both urban streets and rail. Data the BBC obtained shows that only 16 of the 36 three-carriage units have passed the statutory testing that proves they are safe on the UK rail network. Twenty are still waiting for scrutiny by the rail regulator. Testing on some began in 2024, and the Freedom of Information response shows it can take anywhere from six weeks to two years.

The six in passenger testing have at times been pulled from service for what TfW called teething issues and early reliability challenges, caused by software problems. Price called the delays frustrating but not unexpected. He said he does not accept there is a problem with the tram-trains themselves, but that software is the biggest issue, because one large package controls the whole fleet and TfW has automated as much as it can. Once it works, he argued, improvements can be pushed out through software rather than hard engineering, which would be cheaper, quicker and more reliable. TfW did not launch the vehicles with a big fanfare, Price said, and chose customer testing because it feared they might have to come out of service. His benchmark is trains that work 100% well, 100% of the time; the valleys network is already achieving 95% on-time reliability.

Stadler says it is working closely with TfW on minor issues in what it calls one of the UK's most advanced battery tram-trains, and describes software updates as normal refinements during fleet introduction. Price recently met Stadler's chief executive in Germany to try to speed things up. TfW also points to electrification: the line infrastructure was only finished in March, held up by Covid and the supply chain effects of the war in Ukraine.

Price says the delay has one explanation: the new class 756 trains, introduced on the valleys line in 2024 after years of complaints about old rolling stock, arrived earlier and ran more reliably, so there was no chance to test the tram-trains against the original date. Getting new trains running and maximising value for money, he said, was the priority.

The rail engineer and broadcaster Gareth Dennis calls it a pretty ambitious project. The whole network is electrified, but only two-thirds has traditional overhead wires; batteries cover the rest. TfW says that saved about £400m and years of time. Dennis fears corners are being cut, and notes this is the first deployment to combine a tram, a train, a battery and discontinuous electrification, which is why it is not common. TfW replies that the technology already works on the larger 756 trains.

Reform's shadow transport minister, Jason O'Connell, asked why most of the units are sitting in a depot gathering dust, and said taxpayers deserve to know how delays turned into years. The Welsh government says TfW remains on target to finish the rollout by the end of next year.

What has to happen first is the doubling from two to four trains an hour between Cardiff and Aberdare, Merthyr Tydfil and Treherbert, a pledge also first made for 2022. Price says several hundred crew must be trained and signalling work done at Cardiff Queen Street, and he fully expects four trains an hour by the end of next year.