(1) The provisions of section 40-1911, Idaho Code, shall not apply to those segments of the interstate and primary system of highways which traverse and abut on commercial, business or industrial zones within the boundaries of incorporated cities, wherein the use of real property adjacent to and abutting on the interstate and primary system of highways is subject to city or county regulation or control, or which traverse and abut on other areas where the land use is clearly established by state law or county zoning regulation, as industrial, business or commercial, or which are located within areas adjacent to the interstate and primary system of highways which are in unzoned commercial or industrial areas as determined by the department from actual land uses. The department shall determine the size, lighting and spacing of signs in the zoned and unzoned industrial, business or commercial areas.
(2)  For the purpose of this chapter, areas abutting interstate and primary highways of this state which are zoned commercial or industrial by counties and cities shall be valid as commercial or industrial zones only as to the portions actually used for commerce or industrial purposes and the land along the highway in urban areas for a distance of six hundred (600) feet immediately abutting to the area of the use, and does not include areas so zoned in anticipation of such uses at some uncertain future date, nor does it include areas zoned for the primary purpose of allowing advertising structures. All signs located within an unzoned area shall become nonconforming if the commercial or industrial activity used in defining the area ceases for a continuous period of six (6) months.