Snow and sub-zero temperatures have made driving dangerous The Met Office has issued a severe weather warning as freezing conditions continue to make travel dangerous.
Weather experts said many untreated roads in the Highlands and Western Isles would become very icy, especially across the coastal west.
Across north east Aberdeenshire and around Aberdeen frequent snow showers will be heavy at times with further fresh falls of up to 5cm in places.
Travellers were advised to take extra care, especially on untreated roads.
The Met Office said overnight temperatures in the Highlands and Islands could drop to -11C.
For Christmas Day it has forecast sleet and snow showers, with the potential for the heaviest falls over Lochaber.
Overnight temperatures in Aberdeenshire and Moray could fall to -10C, the Met Office said.
It said it would remain very cold on Christmas Day.
Aberdeenshire Council said road crews were again out in force, with the lowest recorded temperature overnight -11C at Tillyfourie, near Inverurie.
Northern Constabulary said all trunk routes into the Highlands and Islands were open and in reasonable condition.
However, police said very low temperatures across the region meant there was “a significant risk of black ice”.
Four people were killed in crashes on Scotland’s roads on Thursday.
Two of them were killed in a two-car collision near the Highland village of Croy.
On the railways, ScotRail urged train passengers to check services before travelling. It said it was constantly reviewing its temporary timetable and, where possible, it would reinstate normal services. Latest updates will appear on the journey check website.
Scotrail said Aberdeen to Inverness was expected to run as booked.
Inverness to Wick will not call at Thurso.
Scotrail said Edinburgh Waverley to Glasgow Queen St services remained reduced to half-hourly service.
However, it announced additional services would run in the evening.
There will be no rail services on Christmas Day and a limited Strathclyde service on Boxing Day.
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