Thousands of schoolchildren are having a day off, with fresh falls of heavy snow affecting parts of Scotland, Northern Ireland and northern England.
UK temperatures remain sub-zero - overnight Scotland hit -17C (1F).
The Met Office is warning of icy roads across much of the UK. Central Scotland police advise essential journeys only.
Scotland's Transport Minister Stewart Stevenson has apologised after hundreds of drivers were stranded overnight, with the central belt particularly badly hit by snow.
Some 150 pupils, parents and staff had to spend the night in a South Lanarkshire school.
Meanwhile, a dog walker in Saltburn, Cleveland, was rescued by a police helicopter after falling down a steep snow-covered slope in a densely-wooded area.
Officers in the helicopter used a thermal imaging camera to spot the 51-year-old woman after she slipped off the footpath.
Commuters have been enduring another day of travel disruption:
- The M8 westbound between Edinburgh and Harthill will remain closed overnight
- Belfast International and Edinburgh airports are open but passengers are advised to check for delays with airlines. Glasgow is not currently taking in-bound flights and all flights may be subject to delay and cancellation
- On the railways, Scotland's routes are all affected. Many are without trains - or replacement buses - altogether
- Services in and out of London's Liverpool Street station were delayed by up to 45 minutes throughout Tuesday morning
- Reduced services are operating on the East Coast Mainline, while several local services in Yorkshire were disrupted
- Transport Scotland warns motorists not to travel unless "absolutely essential"
The AA had attended 7,700 breakdowns by 1100 on Tuesday, having dealt with 24,000 the previous day - more than twice the norm.
Strathclyde Police say they are dealing with more than 1,000 vehicles which have either been abandoned or are stuck in the wintry conditions, with 1,000 officers out working in the snow.
Many drivers were stuck overnight on the M8 after heavy snow caused severe disruption to the route that links Glasgow with Edinburgh.
Traffic was also brought to a standstill on the M80, which runs through central Scotland, with drivers advised to stay with their vehicles.
Among them was Alan Towle, who set out on a journey from work that normally takes 45 minutes at 1500 GMT on Monday, only to arrive home nine hours later.
"It was pretty horrific... an absolute farce. There was no evidence of anyone official doing anything," he said.
"Police should have been helping gritters and ploughs clear both lanes on the opposite carriage to get smaller vehicles moving."
Mr Stevenson told BBC Radio Scotland the authorities had been caught out by the severity of the weather yesterday but queried the advice given by the government's forecasters, which he said differed from that of other experts.
"We prepared for one set of weather yesterday morning - we had weather greater than we were ready for."
He insisted staff had been making "quite heroic efforts", but added: "Today we're now facing temperatures so low that salt is no longer working on the network.
"We've actually seen snowploughs damaged by the solidity of the ice on the M8."
However, Scottish Liberal Democrat leader Tavish Scott said it was "unbelievable" to blame forecasters' advice.
"I was briefed by the Met Office in my living room courtesy of my television," he said.
"This excuse is even more slippery than the roads."
Police say people who have abandoned vehicles should not return to them unless advised to do so. Some vehicles have been removed already and officers are contacting owners to tell them how to get them back.
Temperatures were recorded as having dropped as low as -17C overnight in Strathallan, near Perth, and -14C (7F) at Sennybridge in Powys and Castlederg, Tyrone, and Scampton, Lincolnshire.
BBC forecaster Jay Wynne said icy roads would be a problem, particularly in Northern Ireland and the central lowlands of Scotland.
Cumbria and northern Lancashire could see 2-5cm (1-2in) of snow during Tuesday, while dense freezing fog would linger across the Midlands and southern England, he added.
Meanwhile, the RSPCA says it has had to deal with 5,476 rescues, complaints and collections across England and Wales during the recent cold weather.
Its 425 inspectors, animal welfare and animal collection officers dealt with 2,098 animal rescues and collections and 3,378 animal welfare complaints between 26 November and 3 December.