Wash. Rev. Code § 47.22.010
There is hereby established the east Pacific highway which shall be composed of the following existing highway routes: Beginning on state route number 5 at or near Centralia; thence by way of state route number 5 to its junction with state route number 12 or by way of state route number 507 between Centralia and Tenino; thence on state route number 507 to Roy junction with state route number 7; thence on state route number 7 to a junction with state route number 512; thence on state route number 512 to Puyallup; thence on state route numbers 410 and 167 to Sumner, Auburn, Kent and Renton; thence on state route number 405 to Kirkland; thence on state route number 405 north to a junction with state route number 522; thence on state route number 522 to a junction with state route number 9 northeast of Woodinville; and thence on state route number 9 to Snohomish, Arlington, Sedro Woolley, and to a junction with state route number 542 at Deming; thence westerly on state route 542 to a junction with state route number 9 at Lawrence; thence on state route number 9 via Sumas, to the Canadian international boundary.
RCW 47.22.010