It is affectionately known as the “Flying Banana”, a special train packed with hi-tech equipment that tours the network checking for track faults.
However, the yellow carriages and their locomotive have themselves slipped up, causing hours of delays to passengers.
Figures provided under freedom of information laws showed Network Rail’s “new measurement train” – the railway equivalent of an MRI scanner – had caused disruption at least 23 times in the past three years.
The train is designed to spot faults so they can be fixed before they get worse and disrupt services – and it travels at high speed to avoid slowing other trains.
But the Network Rail figures revealed the Flying Banana had suffered from a series of breakdowns and other problems, such as its crew turning up late, which have held up travellers.
The biggest single incident caused more than three-and-a-half hours of delays near the Craigentinny depot, on the East Coast main line, last May.
In the latest incident, 12 ScotRail services had to be cancelled and others were delayed after the train detected a fault then spilled fuel in March. That incident was not included in the figures because the delays caused are still being calculated.
The leak happened on one of the busiest sections of the network – the steep tunnel down into Queen Street station in Glasgow.
This caused “poor railhead conditions”, making it difficult for other trains trying to go up the slope.
The train’s sophisticated cameras and thermal equipment enable it to record images of track a fraction of a millimetre long, at the rate of 70,000 pictures a second, while travelling at up to 125mph. Details of faults are sent to engineers to check and fix.
Rail development campaigners Railfuture said the train had a good record overall.
Spokesman Bruce Williamson said: “This train does great work in monitoring the condition of the track and helping to keep the network running smoothly. It’s inevitable that occasionally, as with any other train, things go wrong and it causes some sort of problem. In the real world, we shouldn’t be surprised if the Flying Banana occasionally drops a bit of a banana skin itself.”
A Network Rail spokesman said: “Our fleet of measurement trains perform a vital role in keeping the railway moving and in driving up performance by quickly identifying faults.”