There are delays on the Dart line and northern commuter rail routes this morning due to a technical fault.
Iarnród Éireann said there are delays of between 10 and 15 minutes following a train fault at Kilbarrack station on Dublin's north side.
It apologised for the inconvenience caused to passengers.
Meanwhile, there are traffic restrictions in place in some towns and cities to facilitate Car Free Day.
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In Dublin, Merrion Square West is closed from 7am to 7pm and there will be food stalls and entertainment throughout the day.