(1) The secretary of transportation shall have the power and it shall be its duty to adopt and designate a uniform state standard for the manufacture, display, erection, and location of all signs, signals, signboards, guideposts, and other traffic devices erected or to be erected upon the state highways of the state of Washington for the purpose of furnishing information to persons traveling upon such state highways regarding traffic regulations, directions, distances, points of danger, and conditions requiring caution, and for the purpose of imposing restrictions upon persons operating vehicles thereon. Such signs shall conform as nearly as practicable to the manual of specifications for the manufacture, display, and erection of uniform traffic control devices for streets and highways and all amendments, corrections, and additions thereto.
(2) The department of transportation shall prepare plans and specifications of the uniform state standard of traffic devices so adopted and designated, showing the materials, colors, and designs thereof, and shall upon the issuance of any such plans and specifications or revisions thereof and upon request, furnish to the boards of county commissioners and the governing body of any incorporated city or town, a copy thereof. Signs, signals, signboards, guideposts, and other traffic devices erected on county roads shall conform in all respects to the specifications of color, design, and location approved by the secretary. Traffic devices hereafter erected within incorporated cities and towns shall conform to such uniform state standard of traffic devices so far as is practicable. The uniform system must allow local transit authority bus shelters located within the right-of-way of the state highway system to display and maintain commercial advertisements subject to applicable federal regulations, if any.
(3) The uniform system adopted by the secretary under this section may allow signs, banners, or decorations over a highway that:
(a) Are in unincorporated areas;
(b) Are at least twenty vertical feet above a highway; and
(c) Do not interfere with or obstruct the view of any traffic control device.
The department shall adopt rules regulating signs, banners, or decorations installed under this subsection (3).