Up to 110,000 passengers are expected to be affected by the train drivers dispute this evening.
DART services will be reduced by half this evening and commuters are being urged to use alternative transport. A full list of cancelled services is available on the Iarnród Éireann's website, www.irishrail.ie.
Stations at Dundalk, Drogheda, Connolly and Fairview remain under pickets this evening and trains to Drogheda, Dundalk, Maynooth and Arklow affected.
Inter-city services between Dublin and Belfast, Sligo and Rossare are also disrupted.
Today's action is the first of nine rolling one-day strikes by ATGWU members over the next three weeks.
Tomorrow, pickets will be placed at Cork, Mallow, Waterford and Inchicore depot, and Limerick, Athlone and Portlaoise stations.
Major roads into Dublin were badly affected by the strike this morning, AA Roadwatch said.
Worst-affected was the N1 from Drogheda, the N2 from Slane and the N4 from Maynooth. In the city the Rock Road and Cabinteely bypass were particularly busy and traffic is expected to be heavy again this evening.
Iarnród Éireann's customer information line (1850 366 222) is open until 9 p.m. today.
