The rail tunnel at Glasgow Queen Street has reopened after being closed for 20 weeks during improvement works.
The tunnel closure was part of a wider project to revamp Queen Street and allow longer, faster trains to run from the station.
During the works, trains to Stirling, Edinburgh and Aberdeen were diverted to low-level platforms or Glasgow Central.
The £60m revamp of the tunnel has been completed a day earlier than originally planned.
ScotRail said the closure was necessary to enable the renewal of 1,800m of existing concrete slab track formation, which carries the rails through the 918m tunnel.
The project involved the removal of 10,000 tonnes of existing concrete slab and the installation of 4,000m of new rails.
The floor of the tunnel has been lowered and electric pylons also installed.
Transport Minister Humza Yousaf said: "I am pleased to see the work on the Queen Street tunnel completed ahead of schedule and on-budget.
"This has been an unprecedented project, both in engineering terms and in the scale of the operation required to keep people moving and services diverted via the underground platforms during the works.
"This is a key milestone in our programme of investment for Scotland's railways and literally paves the way for the introduction of a new generation of electric trains."
Phil Verster, managing director of the ScotRail Alliance, said: "The successful, early delivery of this project will allow us to introduce faster, longer and greener trains on the main Edinburgh-Glasgow line - delivering thousands of extra seats, shorter journey times and improved accessibility for customers."
Work to redevelop Glasgow Queen Street station is due to begin later this year with completion expected in 2019.