A £1 billion fleet of commuter trains has been left in storage for years after trade unions objected to the size of their windscreen wipers, according to a report in The Telegraph.

The 90 Arterio trains were purchased by South Western Railway (SWR) to replace the 40-year-old ex-British Rail carriages that are still in use on the commuter lines out of London Waterloo.

However, the fleet has been delayed from entering full passenger service for years, partly because Aslef, the train drivers’ trade union, raised objections to the size of the windscreen wipers.

Unions claimed the wipers were so big they blocked drivers’ views of the trackside signals that tell trains when to stop and go.

The Arterio train has one of the largest windscreens of any modern UK train, with other designs restricting the driver to a small side window.

Issues with couplers used to connect the trains together, electrical traction equipment, and even cab doors that "proved difficult to open" have also delayed the Arterios’ entry into use, according to Rail magazine.

SWR has acknowledged the flaws and said it aims to get 10 of the new trains into service within the next four months, once the company’s 700-plus drivers have been trained on them.

SWR sources said Aslef dropped their objections to the trains as part of a deal for a 15 per cent pay rise with Louise Haigh, the Transport Secretary, earlier in 2024.

Most of the Arterio fleet is now stored in depots around the country, including at Eastleigh in Hampshire, instead of being driven on commuter services.

An SWR spokesman said in The Telegraph: "As is well documented, introducing the Arterios has been a major and complex project, introducing both a new fleet and method of operation, while facing extensive production and software issues and all against a backdrop of Covid and industry recovery.

"Our first train entered customer service earlier this year and, following good progress on training colleagues and the trains performing well, we are now expanding the phased rollout of the 90-strong fleet, as evidenced by the new service to Shepperton this week.

"This is an important milestone on the Arterio programme and another step toward the full rollout of the fleet of 90 Arterio trains that are set to transform capacity and comfort on SWR’s suburban network.

"We’re looking forward to introducing more Arterio services and will be sharing the wider rollout plan in due course."