cost
(13) “net investment” in a project means the actual legitimate original cost thereof as defined and interpreted in the “classification of investment in road and equipment of steam roads, issue of 1914, Interstate Commerce Commission”, plus similar costs of additions thereto and betterments thereof, minus the sum of the following items properly allocated thereto, if and to the extent that such items have been accumulated during the period of the license from earnings in excess of a fair return on such investment: (a) Unappropriated surplus, (b) aggregate credit balances of current depreciation accounts, and (c) aggregate appropriations of surplus or income held in amortization, sinking fund, or similar reserves, or expended for additions or betterments or used for the purposes for which such reserves were created. The term “cost” shall include, insofar as applicable, the elements thereof prescribed in said classification, but shall not include expenditures from funds obtained through donations by States, municipalities, individuals, or others, and said classification of investment of the Interstate Commerce Commission shall insofar as applicable be published and promulgated as a part of the rules and regulations of the Commission;