Wash. Rev. Code § 81.80.195
This chapter shall exclusively govern the liability insurance requirements for motor vehicle common and contract carriers. Any motor vehicle that meets the public liability requirements prescribed under RCW 81.80.190 shall not be required to comply with any ordinances of a city or county prescribing insurance requirements.
RCW 81.80.195
Policy-1989 c 264: "The state legislature has prescribed what requirements are necessary for public liability insurance for motor vehicle common and contract carriers to adequately protect both public and private property, both real and personal. It is therefore necessary and desirable for the state to prevent each city or county from applying its own separate insurance regulations in addition to those required by the commission." [ 1989 c 264 s 1.]