Driving time limits for gritters have been suspended The wintry weather is causing further disruption across Scotland as overnight temperatures dropped as low as -20C in some places.
Icy roads are widespread and some schools are closing for a fifth day.
These include all schools in Fife, East Lothian, Midlothian, West Lothian, North Lanarkshire and the Scottish Borders.
Transport Scotland urged drivers who have to travel to make robust plans in advance.
And Chief Constable Kevin Smith, chairman of the Acpos road policing business area, added: “Motorists need to pay extra attention and be prepared to adapt to changing conditions.
“Even the most experienced motorists can find themselves getting into difficulties when the roads are icy or covered in snow.
“Our advice is to consider if your journey is absolutely necessary and if you must drive then ensure that you and your car are adequately prepared for the journey ahead.”
On Thursday night more than 200 train passengers became stranded for almost five hours near Forgandenny, outside Perth.
ScotRail said the incident happened when the freezing temperature caused the loss of air pressure required to work the systems on the Glasgow to Aberdeen train.
The train left Glasgow at 1542 GMT. The passengers were not on the move again until just before 2130 GMT after a replacement train was sent.
A ScotRail spokesman urged customers to check its website before setting out and to allow more time for journeys.
The regulations dictating how long snow clearance drivers can be behind the wheel were suspended on Thursday due to the severe and prolonged weather conditions facing Scotland.
First Minister Alex Salmond said: “By temporarily suspending time limits on driving time for gritters, we can ensure more roads are kept clear and give local authorities greater flexibility to deal with these difficult conditions and keep Scotland moving.”
He told the Scottish Parliament that Scotland had two months’ supply of grit, even with heavy use.
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