Met Éireann has issued a warning for dense fog across the country this evening and tonight.
The Status Yellow warning came into effect at 4pm and is in place until 10am on Saturday morning.
Temperatures are also forecast to drop to between 0 and 3C tonight, leading to a risk of ice on roads.
The Met Office have also issued a yellow warning for fog or freezing fog across much of Northern Ireland.
That warning came into effect at 7pm and is in place until 11am.
The fog is likely to impact on one of the busiest travel days of the year, as people begin to travel home for Christmas.
The Road Safety Authority has urged motorists to use their fog lights when driving in dense fog, and to remember to turn them off when the fog clears.
Motorists are urged to slow down and drive at a safe distance from the car in front of you.
Fog lights must only be used in dense fog or falling snow. Please remember to turn off your fog lights when the fog or snow clears. pic.twitter.com/XgQVVilTF8
— RSA Ireland (@RSAIreland) January 5, 2018
AA Ireland is urging motorists to be extra cautious as the Christmas exodus begins.
Commuter traffic on main routes around the country will peak today and into the weekend.
While 23 December is usually the busiest day for travel, AA Ireland said that because Christmas Day falls on a Wednesday this year many people are expected to take Monday and Tuesday off and begin travelling home from today.
