Motorists have been warned to take extra care after heavy rain caused severe flooding.
Gardai urged all road users to exercise extreme caution, drive with lights on and allow plenty of time for their journeys.
Flooding caused problems for rush-hour commuters in many parts of Leinster and some areas of Munster.
In north Dublin, the Ballyboughal to Oldtown road, near Blake's Cross, and the Old Pormarnock Road are said to be impassable, while there is flooding on the M1 near Donabate and Airside Retail Park.
James Larkin Road between Greendale and Watermill Road - known as Black Banks - is flooded and drivers face problems in Alymer Road, Newcastle, and the N32. Several roads in Wexford town are impassable due to flooding and on the N11 Wexford/Dublin road there has been a minor landslide just north of J14 Cullenmore. There is also flooding around parts of Wicklow and Waterform, with the N25 deemed impassable.
And in Cork motorists are being told to avoid the local road between Fermoy and Ballyhooley as well as the local road between Mitchelstown and Araglin.
Dart and train services between Greystones and Dalkey have been cancelled because of severe flooding at Sandycove.
AA Roadwatch said motorists should slow down and increase their braking distance.
"Only drive through water if you know it's not too deep for your car," the organisation said. "If you have to drive through water, drive through the centre of the road as that is the highest point but only when it's safe to do so."