Wash. Rev. Code § 47.08.120
There is hereby created in the state treasury a state fund to be known as the "transportation equipment fund," the same to be used by the department of transportation as a revolving fund to be expended for salaries, wages and operations required for the repair, replacement, purchase and operation of equipment and for purchase of equipment, materials and supplies to be used as follows:
The transportation equipment fund shall be credited, in the case of equipment, with a reasonable rental assessed upon the use of such equipment by the various state departments, and in the case of materials and supplies, with a reasonable charge for such materials and supplies. Such credit for rental and charges for materials and supplies shall be charged against the proper appropriation therefor.
Equipment may be rented and materials and supplies may be sold out of this fund to any federal, state, county or city political subdivision or governmental agency. The terms and charges for such rental and the prices for such sale shall be solely within the discretion of the department of transportation and its determination of the charge for rental or sale price shall be considered a reasonable rental charge or a reasonable sale price. Any political subdivision or governmental agency shall make payment for such rental or for purchase of such materials or supplies directly to the transportation equipment fund at the office of the department of transportation at Olympia.
RCW 47.08.120