The alert, for Leinster and Munster, is in place until midday.
A Status Yellow fog warning for Leinster and Munster has been issued by Met Éireann.
Fog and freezing fog is affecting many areas this morning, fog will be slow to lift and may linger locally beyond mid-day when the warning is due to be lifted.
Brian Farrell of the Road Safety Authority is urging motorists exercise extreme caution this morning.