Commuters are bracing themselves for travel chaos as forecasters predict temperatures will plummet to minus 10C overnight.
Road conditions have remained hazardous nationwide, with further snow showers expected across the north, south and east of the country.
AA Roadwatch warned roads will be a treacherous in the morning as air temperatures, which barely got above freezing during the day, drop.
Dublin Bus and Bus Eireann said driving conditions were extremely difficult and warned of disruptions to services.
Met Eireann issued a severe weather warning and said the bitterly cold snap will continue for the next four days at least, with sharp or severe frosts, icy roads and some freezing fog at times.
Motorists were warned not to make unnecessary journeys and to reduce their speed and keep a safe distance from other vehicles.
Several roads are treacherous while the Sally Gap and the Wicklow Gap are impassable. Meanwhile Irish Rail said DART and commuter services are expected to operate as normal.
A spokesman said line inspection, signalling maintenance and fleet maintenance teams have ensured that all routes are open and fully operational. "We will continue to work to provide a full service throughout this cold spell," he added.
Dublin City councillor Kevin Humphreys said the National Emergency Response Committee must meet to ensure state agencies are ready to co-ordinate efforts.
"Preparations must be made now to ensure that there is an efficient and effective response should this current cold weather stay," he said. "We need to prepare for the worst and hope for the best."