Black ice on the Rimutaka Hill road between Featherston and Upper Hutt is making driving conditions treacherous.
Police spokesperson Inspector Ken Climo says there have been several calls from drivers whose vehicles have slipped on the ice overnight on Tuesday.
He says people who travel the route regularly usually know where black ice is likely to form, but that has changed with recent road works and drivers must travel to winter driving conditions.
Contractors are assessing the conditions and will decide whether to treat the roads with grit or chemicals to make driving safer.
