This morning's train disruption is one of the worst Irish Rail has ever experienced.
Over 20 thousand passengers were delayed when services were suspended at Heuston Station.
The signalling system - which ensures the safe movement of trains - suffered a major fault shortly before 6am - and all trains in and out of the station were suspended for a time.
Services resumed after a temporary manual signalling system was put in place.
The Westport and Galway services are operating, but there were some knock-on delays this morning.