Gritters across Norfolk will have to precisely time their journeys over the next few days to prevent black ice, the county council has said.
Thursday's temperatures are set to drop to -7C with rain and snow forecast.
A council spokesman said rain could wash salt off the roads, then freeze and cause black ice.
Highways maintenance manager Nick Tupper, said: "The forecast weather pattern is one of the hardest for us to deal with."
"Timing the gritting run will be critical. The roads will already have been treated before the rain and snow arrives, and we will have crews on standby ready to start gritting as soon as it clears."
Drivers are being urged to be extremely cautious.