Rail passengers in the west of England have been asked to check timetables before they travel due to engineering work beginning on Christmas Eve.
Network Rail is carrying out £25m of improvements on the Great Western network over the festive season as part of ongoing electrification work.
Some Great Western Railway (GWR) trains will be disrupted into the new year.
Track renewal at Westbury means the line between Trowbridge and Warminster will be closed until 3 January.
Work at Severn Tunnel Junction will also take place until 1 January, and rail replacement buses will be in operation.
GWR services will end earlier than usual - between 21:30 and 22:30 GMT - on Christmas Eve.
Sarah Fraser from Network Rail said the Westbury engineering works, which began on Sunday, would make the track outside the station "much more robust".
"At the moment there is a speed restriction on it, so sometimes it's difficult for us to run the timetable to time.
"That should get easier.... and we should see fewer faults with the signalling systems."
Mark Langman from Network Rail said: "Owing to fewer passengers travelling at Christmas, we have an opportunity to carry out extensive improvement work with less disruption.
"We have dozens of projects which will be completed on Christmas Day and Boxing Day with no impact on train services.
"These projects will enable us to keep operating a safe, reliable railway for the communities and economies which we support."