Months of bus replacement misery for rail passengers in the north-east is set to end.
Network Rail is carrying out significant improvements on the line between Aberdeen and Inverness to increase the capacity and upgrade the service.
The rail authority had closed sections of the line between the two cities as part of a £300 million project to dual the track.
Some parts of the line are currently single track, meaning trains are not able to pass each other.
Work started in May, with bus-replacement services throughout the line, including a three-day service between Aberdeen and Inverness.
However, rail passengers will finally swap the road for the track tomorrow.
A Network Rail spokesman said: “The double-tracking and resignalling works are all progressing well and we expect to be able to reopen the line as planned from start of service tomorrow morning.”
Network Rail bosses hope the project will also improve the reliability of services.
The double-tracking of the section is being carried out in preparation for the construction of a new station at Kintore, due to open in time for new timetables being introduced next May.
In total, 18km of new track has been laid, along with 32,000 sleepers and 72km of cables.
Signalling and bridges are being upgraded too, with the Don Viaduct between Dyce and Inverurie strengthened to cope with the increased load. The bridge was built in 1881.
Around 65,000 tonnes of ballast will be used for the whole project, with 76,000 tonnes of earthworks being removed.
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The benefits of the upgraded line are expected to be seen by commuters from December 2019.
A ScotRail spokesman said: “The next timetable change is in December.
“More InterCity trains will be introduced on an ad hoc basis as our supplier’s refurbishment programme progresses.”
The Network Rail spokesman added: “The Aberdeen to Inverness improvement project is a Scottish Government-funded project to upgrade the railway infrastructure between the two cities.
“Passengers will benefit from the introduction of hourly service between Inverness and Elgin extra 1,300 additional seats each day.
“The majority of Aberdeen to Inverness services will be high-speed trains providing 1,400 extra seats each day.”