Wash. Rev. Code § 81.28.010
All charges made for any service rendered or to be rendered in the transportation of persons or property, or in connection therewith, by any common carrier subject to regulation by the commission as to rates and service, or by any two or more such common carriers, must be just, fair, reasonable, and sufficient.
Every common carrier shall construct, furnish, maintain and provide, safe, adequate, and sufficient service facilities and equipment to enable it to promptly, expeditiously, safely, and properly receive, transport, and deliver all persons or property offered to or received by it for transportation, and to promote the safety, health, comfort, and convenience of its patrons, employees, and the public.
All rules and regulations issued by any such common carrier affecting or pertaining to the transportation of persons or property must be just and reasonable.
RCW 81.28.010