Heavy snow has hit many parts of the country overnight.
Some of the worst-affected areas are along the east coast with roads in Dublin, Kildare, Wicklow and Louth badly hit.
The AA says conditions on the southside of Dublin are much worse than yesterday morning, while gardaí are advising motorists in Wicklow to avoid driving on higher ground.
Secondary routes in many counties are also to be avoided.
Motorists are advised to only drive when necessary and to take public transport where possible.
There are about 100,000 kilometres of roads in Ireland, of which the top 5% (national roads and motorways) carry 50% of the traffic.
Sean O'Neill from the National Roads Authority said those main routes and public transport corridors were given priority in terms of gritting and being kept clear of snow.
Dublin Airport is open and fully operational and there appear to be no delays at present in Shannon and Cork as yet.
Irish Rail is expecting to run all of its services again today, as is the Luas in Dublin.
Dublin Bus is running most of its routes but it is experiencing some delays and schedule changes.
Ferries are also scheduled to operate as normal.
Bus Éireann said the vast majority of its services around the country were operating as normal with some delays and diversions in affected areas. The affected routes are:
2 Dublin Airport –Rosslare – early morning services cancelled
109A Navan-DCU – early morning services did not operate
161 Dundalk-Newry – 0800 cancelled
168 Dundalk-Annagassan - cancelled
175 Monaghan-Cavan – cancelled