Iowa Code § 313.18

When claims for labor, freight, or other items which must be paid promptly are presented to the said department for payment, the said department may direct that warrants in payment of said claims be drawn on said primary road contingent fund. Such warrants when so drawn and signed by the director of the department of administrative services, shall be honored by the treasurer of state for payment from said contingent fund. The primary road contingent fund shall be reimbursed for expenditures made by the state department of transportation from the fund to which the expenditure should be properly charged.