TEMPERATURES are expected to plummet to as low as minus four degrees overnight as the winter's first cold snap hits the country.
Motorists have been warned to take extra care as widespread sharp or severe frost could cause dangerous icy patches on untreated road surfaces.
Local authorities are on standby to spread salt as sub zero temperatures hit inland areas.
Met Eireann said fog is also expected in parts of the midlands and the east.
Road Safety Authority (RSA) issued an alert for road users in icy and fog conditions.
"If the road looks polished or glossy it could be black ice, one of winter's worst hazards," it said.
"It is nearly transparent ice that often looks like a harmless puddle or is overlooked entirely.
"Watch out for black ice, especially in sheltered/shaded areas on roads, under trees and adjacent to high walls."
It warned drivers to get their tyres, including a spare, examined and replaced if needed and to use dipped headlights.
Windows and mirrors should be cleaned before a journey and motorists should manoeuvre gently and give themselves time to stop.
Elsewhere pedestrians and cyclists were also told to look out for icy and slippery patches.
"Many slips and falls happen in places people regard as safe and secure, typically outside their front door, on the door step, on the path or while getting out of the car," the RSA added.
"If you are out walking in icy conditions wear appropriate footwear, don't walk with your hands in your pockets, walk with your hands out and wear gloves so you can break your fall if you do slip.
"Visibility is reduced in fog, hail or rain so wear high visibility clothing or carry a torch and if you cycle make sure your bike is fitted with lights front and rear."
Temperatures are expected to be below normal for the next 10 days and night frosts are likely.
The NRA said there are 150,000 tonnes of salt in the country to treat national roads, and 60,000 tonnes for key local and regional routes.