AA Roadwatch is warning of extremely icy roads in west Donegal.
The alert has been issued to motorists approaching Letterkenny from Meena Cross, Glenswilly and Meenatinny.
Donegal County Council treated the roads this morning but drivers were advised to avoid taking any unnecessary journeys.
At one point there were at least 100 vehicles stranded on the route.
P&O Ferries said this morning's 7.15am express sailing between Larne and Troon in Scotland was cancelled.
The return sailing at 10.05am was also cancelled.
Delays on the Larne to Cairnryan service were also reported.
Passengers were being advised to contact P&O to make alternative arrangements.
