Wash. Rev. Code § 81.44.010
Whenever the commission, after a hearing had upon its own motion or upon complaint, finds that any equipment or facility for use by any common carrier in, or in connection with the transportation of persons or property, ought reasonably to be provided, or any repairs or improvements to, or changes in, any theretofore in use ought reasonably to be made, or any additions or changes in construction should reasonably be made thereto, in order to promote the security or convenience of the public or employees, or in order to secure adequate service or facilities for the transportation of passengers or property, the commission may, after a hearing, either on its own motion or after complaint, serve an order directing such repairs, improvements, changes, or additions to be made.
RCW 81.44.010