Irish Rail is warning passengers to pre-book intercity services this weekend due to a number of concerts and sporting events.
The first swathe of busy trains are expected from Cork and Limerick to Dublin today for the Spice Girls concert tonight.
Trains from both cities between 9am and 2pm today are completely sold out.
Irish Rail said extra trains will also operate for the concert on the Maynooth line and on Dart services from Connolly after the concert.
There is also a Rod Stewart concert in Páirc Uí Chaoimh tomorrow, a Leinster Football Championship match in Portlaoise and racing in the Curragh on Sunday.
Given the extra passenger numbers, Irish Rail said there will be a crackdown on any anti-social behaviour and alcohol is not allowed on Dart and commuter services while some intercity services are also alcohol-free.