Hundreds of drivers have spent the night in their cars after becoming stranded due to heavy snow.
Mountain rescue teams were sent to help those stuck on the M74 in Dumfries and Galloway after severe weather led to closures at Millbank and Beattock.
Traffic Scotland said gritters were working to clear routes, but were hampered by jack-knifed lorries.
Public transport has been disrupted and schools will remain closed in parts of Scotland and Northern Ireland.
A series of weather warnings have been issued, with snow and ice forecast until Friday.
Scotland, Northern Ireland and the north of England are likely to be affected.
The worst problems overnight have been around junction 12 of the M74 in South Lanarkshire southbound and between junctions 14 and 15 northbound. At times the road has been closed altogether.
One driver stuck on the northbound carriageway of the M74, Fergus McCann, said the impatience of other drivers was making things worse.
He told the BBC: “There’s been a fair bit of impatient driving going on.
“People are in one queue, then people are cutting out and trying to go down lanes that clearly are not for driving on.
“It’s not a surprise that you’re getting a few hundred yards down the road and you’re seeing them facing the wrong way.”
Steve Harris became stranded on the M74 at 17:30 GMT and was still stuck between junctions 11 and 12 more than eight hours later.
“I’ve not moved really in the last four hours,” he told BBC Radio 5 live at about 03:00 GMT.
“I’ve managed to get out of my car a couple of times to stretch my legs. The snow is probably between four and six inches deep around the cars.”
A number of schools will remain closed because of the weather conditions.
Scottish Borders Council has said no schools will open in its area.
There were individual closures in South Lanarkshire, East Ayrshire, Stirling, Falkirk and the Highlands.
Snow was still a hazard on urban roads at the start of the rush hour.
Traffic Scotland warned the M8 in Glasgow was restricted eastbound between junction 14 and 15 because of a collision.
Earlier, police in Dumfries and Galloway warned against “all but essential travel”.
Dumfries & Galloway Virtual Operations Support Team – which was set-up to respond to the weather issues in the region – said: “We are working to clear the stuck vehicles and clear the crashes.
“Please remain in your vehicle and signal the mountain rescue team or police if you need any help or contact us via 999.”
Scottish Fire and Rescue’s station manager in Dumfries and Galloway said motorists had been driving “too close behind me” on his way to a crash, despite “blizzard conditions”.
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