Transport disruption follows heavy rainfall warning for Munster and Leinster
Met Eireann has issued a warning for heavy rainfall in Munster and Leinster.
The alert is expected to be in place until tomorrow evening, with up to 40mm of rain and higher in the mountains.
The Western Corridor rail line between Ennis and Limerick remains flooded with bus substitutions in place.
AA Roadwatch Ireland said: "Extremely wet roads have been reported across the country, with risk of frost in parts of the north west.
"Flooding also remains an issue in some parts of the country following the severe weather of earlier in the month."
Several roads are deluged.
Those in counties Galway, Leitrim and Mayo are the worst affected.
There is less severe flooding in counties Clare, Cork, Kilkenny and Tipperary.
Meanwhile, hundreds of people have braved winter temperatures for Christmas Day swims around Ireland.
A large crowd gathered at the 40 Foot, Sandycove, and jumped into the frigid sea.
Many across the country wore Santa hats and costumes.
Beaches in Cork, Dublin and Galway were flooded with intrepid bathers, some raising money for good causes.
Swimmers are being advised that conditions may be more hazardous than normal because of strong tidal streams and rip currents due to a full moon.