There is an orange weather alert in place for fog.
Met Éireann said fog was likely in many places tonight, with greatly reduced visibility.
The alert is in place until 12 noon tomorrow.
Brian Farrell of the Road Safety Authority said the fog could lead to dangerous driving conditions.
"Met Éireann are forecasting widespread fog across the country (and) we're appealiong toall road users to take care given the driving conditions we'll find with dense fog," he said.