The first of ScotRail's new Hitachi trains is to finally enter service on Tuesday - ten months late - The Scotsman has learned.
The Japanese-built class 385 electric train is due to make its passenger debut on the main Edinburgh-Glasgow line on the 0555 from Edinburgh Waverley to Glasgow Queen Street.
The seven-carriage train will operate several other services on the route during the day, but is the only one of the 70-strong fleet yet available.
ScotRail chiefs had originally planned to start running the trains late at night and at weekends to minimise disruption from any breakdowns.
However, they are understood to be confident after months of testing that they are reliable enough to run on Scotland's busiest line at its busiest.
The introduction was delayed after the fleet had to have new windscreens fitted.
That was because drivers complained they could not see signals clearly at night through the original curved screens, which are being replaced with flatter ones.
The trains should have started running on ScotRail's flagship route last September but were initially held up by delays in building the trains and completing electrification of the line.
Humza Yousaf, the then transport minister, blasted the Hitachi delays in May as "just not acceptable".
He revealed said First Minister Nicola Sturgeon had had to intervene several times to get the Japanese firm to "deliver on its promises".
The trains will enable journey times to be cut by ten minutes to 42 minutes.
However, not all services will achieve this by the target date of December.
They will also ease overcrowding by running as up to eight carriages compared to the maximum six of the diesel trains they will replace.
The windscreen problem forced ScotRail to draft in a stand-in fleet for the route because some of its other trains had come to the end of their leases and were transferred to other operators.
The trains will also run on routes across the Central Belt, including to Dunblane and Alloa once electrification of those lines has been completed in December.
They will also operate on the Edinburgh-Glasgow line via Shotts, Edinburgh-North Berwick, Glasgow-Falkirk Grahamston via Cumbernauld, the Cathcart Circle in Glasgow, and the Glasgow to Neilston and Lanark routes.
ScotRail Alliance managing director Alex Hynes said: “I am delighted customers will be able to travel on our new Hitachi class 385 electric trains from next week. This is a significant moment."
Hitachi said 11 of the trains were in Scotland "at various stages of final preparations before entering into service".
A spokesman said: "We also have trains scheduled to travel from Newton Aycliffe [the County Durham factory where they are being built] up to Scotland over the coming weeks.
"At the moment we currently are building a train a week at Newton Aycliffe."
The spokesman said it would "deliver the majority of the fleet by the end of the year".