Passengers travelling on the Edinburgh-Glasgow main line face six weeks of disruption this summer when engineering works force the closure of part of the route.
The Winchburgh tunnel in West Lothian will be closed from June 13-July 27 to allow the installation of power lines as part of a £750 million improvement programme that will deliver faster trains.
Services from Falkirk High and Polmont stations to Edinburgh will be diverted via Dalmeny, near South Queensferry, as a result.
This could mean journey times increase by around 20 minutes and the number of trains stopping at Falkirk stations could be reduced.
The 400-yard-long tunnel was built in 1842 and is being enlarged to accommodate overhead wires.
Network Rail said it was not yet able to detail what disruption to services would be caused by the work, but an update could be expected around late February.
Abellio, the company that will take over the running of the vast majority of Scotland’s trains from April, said it was already making preparations for the tunnel closure.