COMMUTERS are being stuck with Scotland’s most unreliable trains because ScotRail’s plans to swap them with another fleet have been blocked by ministers.
The class 158 diesel carriages, which were once described as "garden shed engineering", have suffered frequent breakdowns.
They also have fewer seats than the extra class 156 diesels which ScotRail had hoped to acquire as substitutes.
The trains’ slow-opening doors also cause delays to passengers getting on and off on frequent-stop commuter routes. By contrast, ScotRail’s existing class 156 trains are its most reliable diesels.
The 20 trains for 20 trains swap would have been with Central Trains, one of ScotRail’s sister companies, which is also part of the National Express Group.
The Birmingham-based company wants ScotRail’s class 158s for longer-distance services because of their higher speeds.
Central Trains uses its class 156s on long-distance routes such as Liverpool-Stansted airport, which have a top speed of only 75mph. The class 158 trains can reach 90mph, but speed limits and frequent stops mean those used by ScotRail never fully exploit that capacity.
However, the Scottish Executive has refused to approve the deal because it is not regarded as good value for money for ScotRail.
A spokeswoman said: "We have turned down the proposal because we were not happy with the financial aspects of it."
The class 158s run on lines such as Fife-Edinburgh, which has one of ScotRail’s worst timekeeping records, and between Edinburgh and Dunblane. The trains also operate on some Edinburgh-Glasgow Queen Street services, and on the Inverness-Aberdeen route and north of Inverness.
Class 156s already operate on several ScotRail routes, including Edinburgh-Glasgow Central, Glasgow-Mallaig and in south-west Scotland.
ScotRail said it would have to live with the decision. A spokeswoman said: "We are disappointed and will have to look at something else. The class 156s have better reliability, more seating and don’t have the problem of slow door-opening."
She said there was no prospect of another train swap before the end of the current franchise next July.
However, she said the reliability of the class 158s was improving thanks to a 2 million upgrade agreed last year. Wiring and cooling equipment are being enhanced to improve the trains’ performance by a third.
They previously broke down on average every 4,000 miles compared to 10,000 miles among ScotRail’s other diesels. The trains have been plagued with engine, heating and bodywork faults since being introduced in 1990.
The entire fleet was withdrawn at one point after an alternator fell off a train on the Forth Bridge. Other problems have included faulty brakes, stiff suspensions causing cracks in the bodywork and frequent air-conditioning breakdowns.
When the trains first arrived, British Rail initially refused to accept them from the manufacturers, describing their failings as deriving from "garden-shed engineering".