In general. The department shall apportion the value of all public utility companies to the various counties in such a manner as will reasonably reflect the true cash value of the operating property located within each county and taxing district. Since it is impossible to determine with mathematical precision the precise value of each item of property located within each county and taxing district, the department shall apportion the value of operating property on the following basis:

(1) Railroad companies - The ratio that mileage of track, as classified by the department, situated within each county and taxing district bears to the total mileage of track within the state as of January 1 of the assessment year. In the event there exists operating property of railroad companies in counties or taxing districts not having track mileage, the department shall situs such property and apportion value directly on the basis of cost as determined in accordance with the cost approach set forth in WAC 458-50-080(A).

(2) Pipeline companies - The ratio that inch-equivalent of miles of pipeline situated within each county or taxing district bears to the total inch-equivalent of miles of pipeline within the state as of January 1 of the assessment year. In the event there exists operating property of pipeline companies in counties or taxing districts not having pipeline mileage, the department shall situs such property and apportion value to such county or taxing district directly on the basis of cost as determined in accordance with the cost approach set forth in WAC 458-50-080(A).

(3) Telegraph companies - The ratio that the cost (historical or original) of operating property situated within each county and taxing district bears to the cost (historical or original) of all operating property within the state as of January 1 of the assessment year.

(4) Telephone companies - The ratio that the cost (historical or original) of operating property situated within each county or taxing district bears to the total cost (historical or original) of all operating property within the state as of January 1 of the assessment year.

(5) Electric light and power companies - The ratio that cost (historical or original) of operating property situated within each county and taxing district bears to the total cost (historical or original) of all operating property within the state as of January 1 of the assessment year.

(6) Gas companies - The ratio that cost (historical or original) of operating property situated within each county and taxing district bears to the total cost (historical or original) of all operating property within the state as of January 1 of the assessment year: Provided, The value of pipeline shall be allocated on the basis of the ratio that inch-equivalent of miles of pipeline situated within each county or taxing district bears to the total inch-equivalent of miles of pipeline within the state as of January 1 of the assessment year.

(7) Airplane companies - The ratio that cost (historical or original) of operating property situated within each county and taxing district bears to the total cost (historical or original) of operating property within the state as of January 1 of the assessment year: Provided, That the value of aircraft shall be apportioned on the basis of the ratio that landings and take-offs of such aircraft within each county and taxing district bears to the total landings and take-offs within the state during the previous calendar year.