Motorway officials today blamed an "abnormally sharp drop in temperature" for the massive jams on key roads out of London which left thousands stranded in icy weather in cars and lorries overnight.
Gritting vans were unable to complete the salting of motorways north east of London yesterday before the surface froze earlier than forecast, causing accidents which blocked the carriageways, a Highways Agency spokesman said.
"We now know from looking at the data that the road temperatures fell below freezing suddenly," he said.
Drivers on the worst affected route, the M11 out of London, spent yesterday night and much of Friday in their vehicles after police closed the motorway. It did not reopen fully until 4 p.m. today.
The Highways Agency, responsible for motorways and trunk roads, advised drivers in snow-affected areas only to travel if their journey was really necessary.
Forecasters said freezing winds, which originated in the Arctic, would bring more snow overnight north and east of London in Lincolnshire, East Anglia, Cambridgeshire and the east Midlands.
Highways Agency Operations Director David York apologised for the chaos after Transport Secretary Mr Alistair Darling demanded to know why the transport system had become paralyzed so quickly.
Mr Darling said he had asked the Highways Agency, the rail industry, London Underground and local authorities for explanations.
PA