Train services to and through Connolly Station in Dublin remain suspended today due to ongoing signalling work.
Many services will have bus transfers for the work which is part of a €120m project to allow extra services and improve safety.
Barry Kenny, from Irish Rail, says there will also be changes to some schedules for the next three weeks.
He told Newstalk Breakfast: "For the next three weeks, starting tomorrow and through to Friday, November 13th, there will revisions to the DART services, they'll be every 15 minutes instead of every ten minutes.
"The Maynooth M3 parkway, including Longford commuter and Drogheda commuter services, will have a revised schedule.
"Customers who must travel should check those times before travel at IrishRail.ie."
Monday 26th October:
Due to Engineering Works the following service alterations and amendments will occur: pic.twitter.com/ghT5buChaN
— Iarnród Éireann (@IrishRail) October 26, 2020
Mr Kenny said the old electrical mechanical system used for train signalling was being updated to a computerised version and that is why the services have been impacted.
He added: "The easiest way to do this would have been to completely shut down the network at Connolly Station for ten days to commission it fully.
"But obviously, there are critical requirements of us during the weekdays.
"So it has been split into phases over three weekends, this weekend and also the first two weekends in November.
"We will be operating with some of the systems that are part of the overall signalling network out of commission at that time.
"Connolly Station is the busiest in our entire network, the signalling system directs 150,000 trains each year."