In the administration of chapter 47.41 RCW, relating to the regulation and control of junkyards adjacent to highways, the term "unzoned industrial areas" shall be interpreted to mean those areas not zoned by county or municipal code, occupied by three or more separate and distinct industrial activities within a space of five hundred feet and the area within five hundred feet of such activities on both sides of the highway. The area shall be measured from the outer edges of the regularly used buildings, parking lots, storage or processing areas of the industrial activity and not from the property lines of the parcels upon which such activities are located. Measurements shall be along or parallel to the edge of the main traveled way of the highway. The following shall not be considered industrial activities:

(1) Agricultural, forestry, grazing, farming and related activities, including, but not limited to, wayside fresh produce stands;

(2) Transient or temporary activities;

(3) Railroad tracks and minor sidings;

(4) Signs;

(5) Activities more than three hundred feet from the nearest edge of the right of way;

(6) Activities conducted in a building principally used as a residence;

(7) Activities not visible from the traffic lanes of the main traveled way;

(8) Junkyards, as defined in section 136, Title 23, United States Code.