RCW 47.36.110

In order to provide safety at intersections on the state highway system, the department may require persons traveling upon any portion of such highway to stop before entering the intersection, except as provided in RCW 46.61.190. For this purpose there may be erected a standard stop sign as prescribed in the state department of transportation's "Manual on Uniform Traffic Control Devices for Streets and Highways." All persons traveling upon the highway shall come to a complete stop at such a sign, except as provided in RCW 46.61.190, and the appearance of any sign so located is sufficient warning to a person that he or she is required to stop. A person stopping at such a sign shall proceed through that portion of the highway in a careful manner and at a reasonable rate of speed not to exceed twenty miles per hour. It is unlawful to fail to comply with the directions of any such stop sign, except as provided in RCW 46.61.190. When the findings of a traffic engineering study show that the condition of an intersection is such that vehicles may safely enter the major artery without stopping, the department or local authorities in their respective jurisdictions shall install and maintain a "Yield" sign.