RCW 36.79.040 sets forth the apportionment formula to be used in distributing RATA funds to the five regions. Following are the computations used in the apportionment formula:

(1) Computation of land area ratio. The ratio that the total county rural land area of each region bears to the total rural land area of all counties of the state shall be computed from information provided by the office of financial management as of July 1, 1993, and each two years thereafter.

(2) Computation of road mileage ratio. The ratio that the mileage of county arterials and collectors in rural areas of each region bears to the total mileage of county arterials and collectors in all rural areas of the state shall be computed from information shown in the county road log maintained by the county road administration board as of July 1st of each odd-numbered year.