This is actually the case. The method to keep roads open is done firstly by using a snowplough vehicle to push the top layers of snow to the side of the road then grit and salt is sprayed on to the remaining snow on the road (from the back of the snowplough/gritting lorry). For this to work, the temperature has to remain above -5C and the the grit/salt worked into the snow/ice by the vehicle traffic. The problem is that the daytime temperatures have not basically risen above -5C so this process doesn't work even during the day. Night time temperatures were last night getting down to -18C in the affected motorway areas.

Many parts of the motorway network due to yesterdays weather and the inability of the snow ploughs to carry out there work, have now basically left the roads with 2-4 inches of solid accumulated ice in place, which cannot be removed using the conventional snow plough/gritting vehicles. This is why many of the main arterial routes in the country are still closed. They will be for the next 2-3 days until the expected warm front appears. This event will now most likely have a serious knock on effect for supermarket and petrol deliveries in the next week or so, leading to shortages.

http://news.bbc.co.uk/today/hi/today/newsid_9262000/9262838.stm

The UK met weather office needs to take some responsibility here as well. They are continually underestimating the real daytime and night time temperatures. In yesterdays forecast they were only showing the temperature in main coastal city centres, which are far removed from the temperatures in the snow fields in the centre of the country i.e. about 10C colder, which they seem reticent to display on their public weather forecasts.

At least the Scottish Transport minister appears to be a little more contrite this morning. Maybe he has been advised that he will be apologising a whole lot more in the next couple of weeks.

http://www.bbc.co.uk/news/uk-scotland-11936621

There doesn't appear to be any news media reports with regard to any hypothermia deaths last night though.

http://www.bbc.co.uk/news/uk-scotland-11936660