If the sum of the direct freight and the direct passenger expenses is more than 50 percent of the total charges to this account for an accounting division, separate the common expenses on the basis of the directly assigned expenses in this account for the accounting division involved. If the sum of the direct freight and the direct passenger expenses does not aggregate 50 percent of the total charges for an accounting division, the common expenses shall be separated on the basis of a special test. If common expenses exist in an accounting division but the direct expenses are applicable to only one service, i.e., freight or passenger, the common expenses shall be separated on the basis of a special test. If the accounting is performed on a system basis rather than by accounting divisions, follow the intent of the above instructions.