An estimated 10,000 rush-hour commuters were stranded in Dublin last evening after DART services southbound were suspended between Dalkey and Bray, Co Wicklow.
Shankill station reported an overhead line down shortly before 5 p.m. which caused the suspension of services.
"The overhead wires which power the DART trains are badly damaged so there will be no services between Dalkey and Bray for the rest of the evening," a spokesman said last night.
He added that, because both DART and Intercity train services were severely affected by the fallen line, the number of passengers inconvenienced was "between eight and ten thousand".
Iarnród Éireann's bus transfer service was unable to cope with the large numbers of commuters.
Intercity trains were unable to get past the affected stations, while DART services were not resumed.
Passengers bound for Arklow, who were due to leave Connolly Station in Dublin at 5.25 p.m., were delayed until after 7 p.m., when Iarnród Éireann decided to merge them with passengers on the 6.30 p.m Rosslare train which had also been delayed.
The southbound passengers then had to change at Bray onto a train which had come up from Rosslare.
The arrival of the 2.45 p.m. Rosslare to Dublin train was delayed by 1½ hours while the train was stranded in Bray.
Emergency crews were at the scene in Shankill and services are expected to resume as normal this morning.
Iarnród Éireann has launched an investigation into the cause of the fallen line.