Passengers travelling on the Galway to Dublin train in the next two months will have to turn up 25 minutes earlier to catch a bus connection to Ballinasloe.
There will be no trains between Galway and Ballinasloe from Monday mornings until Friday evenings to facilitate an £11 million revamp of the line. Passengers travelling from Dublin will also have to take bus transfers on the final leg of the journey to Galway.
"Our aim is to keep the running of the trains into Dublin as near to the timetable as possible," said Mr Myles McHugh of Iarnrod Eireann. "The most critical thing to people travelling to Dublin is to arrive on time."
The improvement works should be completed in March and should reduce the journey time by about 15 minutes. A revised timetable is available from all Iarnrod Eireann stations on the route.