Road conditions have deteriorated, particularly along the west coast, due to snow and falling temperatures.
Icy conditions continue to make driving hazardous in many areas.
The worst affected routes are in Connacht, Ulster and north Leinster.
Some ferry services have been delayed or cancelled, intending passengers are advised to contact their carriers to check if their sailings are going ahead.
Despite a temporary thaw this afternoon, Met Éireann says temperatures are expected to fall below zero again in the coming days.
Tonight and tomorrow, rain and sleet will move north, and it may fall as snow in mountainous areas and inland counties.
Motorists in Wicklow are advised to avoid the Sally Gap, Glenmalure and Aughavanna areas due to dangerous road conditions.
All emergency services have no access to these areas and people are advised not to travel.
Gardaí in Kerry are asking the public to drive with extreme care on the main Dingle to Tralee road following heavy snowfall.
Motorists are also advised to drive with extra care around Castleisland due to icy road conditions. Road conditions are treacherous on the N21 Castleisland/Abbeyfeale Rd.
In Clare, there are treacherous driving conditions around Feakle, Flagmount and Broadford.
Roscommon drivers are recommended to avoid the Ballaghadereen/Castlerea Rd (R325), the Boyle/Castlerea Rd (R361) and the Boyle/Gorteen Rd (R294).
In Leitrim, secondary roads around Carrick-on-Shannon and Manorhamilton should be avoided.
Sligo motorists are advised that it is still icy on secondary routes around the county with care also advised on main roads.
Hundreds without water in NI
In Northern Ireland, road conditions, particularly in rural areas, remain treacherous.
While the majority of main roads have been treated throughout the current cold snap, the roads service has conceded that it simply does not have the resources to treat smaller, rural routes.
There are reports of elderly people, particularly those living in rural areas, being trapped in their homes.
Up to 400 households have been left without water because of the freezing conditions.
Staff at Northern Ireland Water has set up a major incident room to deal with deal with thousands of calls from the public.
