DART services between Greystones and Dún Laoghaire are back to normal after being seriously disrupted this morning.
An electrical fault in a signalling system at Dalkey Station was blamed for the delays.
Northbound services out of Dún Laoghaire were running as normal.
A spokesman for Iarnród Éireann said: "There was a curtailed service between Greystones and Dún Laoghaire".
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He said trains were running at a rate of about one every half an hour.