The department is hereby authorized, whenever needed, to arrange, with any state-owned or private financing agency, including the Bank of North Dakota, short-term loans in the event that construction funds on hand are insufficient to meet current obligations. Short-term financing as provided herein must be in amounts no larger than can be repaid within four years from     moneys known to be due and forthcoming. In no event may such short-term financing be used in anticipation of increased federal-aid highway grants or increased state highway user revenue funds, nor may such loans be obligated for road construction that cannot be financed from a known source of income.