For the purpose of apportioning urban state highway funds, the urban areas of the state are grouped within five regions of the state as follows:

(1) Puget Sound region shall include those urban areas within the counties of King, Pierce and Snohomish.

(2) Northwest region shall include those urban areas within the counties of Clallam, Jefferson, Island, Kitsap, San Juan, Skagit and Whatcom.

(3) Northeast region shall include those urban areas within the counties of Adams, Chelan, Douglas, Ferry, Grant, Lincoln, Okanogan, Pend Oreille, Spokane, Stevens and Whitman.

(4) Southeast region shall include those urban areas within the counties of Asotin, Benton, Columbia, Franklin, Garfield, Kittitas, Klickitat, Walla Walla and Yakima.

(5) Southwest region shall include those urban areas within the counties of Clark, Cowlitz, Grays Harbor, Lewis, Mason, Pacific, Skamania, Thurston and Wahkiakum.