The division of motor carrier and railroad safety shall have power, after hearing, to require any or all motor carriers to carry a proper and adequate depreciation account in accordance with such rules, regulations and forms of account as the division may prescribe. The division may, from time to time, ascertain and determine and by order fix the proper and adequate rates of depreciation of the several classes of property of such corporation, person or public utility. Each motor carrier shall conform its depreciation accounts to the rates so ascertained, determined and fixed, and shall set aside the moneys so provided for out of earnings and carry the same in a depreciation fund and expend such fund only for such purposes and under such rules and regulations, both as to original expenditure and subsequent replacement as the division may prescribe. The income from investments of moneys in such fund shall likewise be carried in such fund.