The department is authorized to divide or separate any state highway into separate roadways, wherever there is particular danger to the traveling public of collision between vehicles proceeding in opposite directions or from cross traffic, by constructing curbs, central dividing sections, or other physical separations, or by signs, marks, or other devices, in or on the roadway appropriate to designate the dividing line.
The rules governing operation of vehicles on divided highways are contained in Section 21651 of the Vehicle Code.