Wash. Rev. Code § 46.44.093
The department of transportation or the local authority is authorized to issue or withhold such special permit at its discretion, although where a mobile home is being moved, the verification of a valid license under chapter 46.70 RCW as a mobile home dealer or manufacturer, or under chapter 46.76 RCW as a transporter, shall be done by the department or local government. If the permit is issued, the department or local authority may limit the number of trips, establish seasonal or other time limitations within which the vehicle described may be operated on the public highways indicated, or otherwise limit or prescribe conditions of operation of the vehicle or vehicles when necessary to assure against undue damage to the road foundation, surfaces, or structures or safety of traffic and may require such undertaking or other security as may be deemed necessary to compensate for injury to any roadway or road structure.
RCW 46.44.093