Washington Revised Code Title 84. Property Taxes § 84.16.050. Basis of valuation--Apportionment of system value to state

The department of revenue may, in determining the true and fair value of the operating property to be placed on the assessment roll value the entire property as a unit. If the company owns, leases, operates or uses property partly within and partly without the state, the department of revenue may determine the value of the operating property within this state by the proportion that the value of such property bears to the value of the entire operating property of the company, both within and without this state. In determining the operating property which is located within this state the department of revenue may consider and base such determination on the proportion which the number of car miles of the various classes of cars made in this state bears to the total number of car miles made by the same cars within and without this state, or to the total number of car miles made by all cars of the various classes within and without this state. If the value of the operating property of the company cannot be fairly determined in such manner the department of revenue may use any other reasonable and fair method to determine the value of the operating property of the company within this state.