Iowa Code § 313A.13
The revenue bonds may be issued and sold or exchanged by the department from time to time and in such amounts as it deems necessary to provide sufficient funds for the acquisition, purchase, or construction of any such bridge and to pay interest on bonds issued for the construction of any toll bridge during the period of actual construction and for six months after completion thereof. The department is hereby authorized to adopt all necessary resolutions prescribing the form, conditions, and denominations of the bonds, the maturity dates therefor, and the interest rate or rates which the bonds shall bear. All bonds of the same issue need not bear the same interest rate. Principal and interest of the bonds shall be payable at such place or places within or without the state of Iowa as determined by the department, and the bonds may contain provisions for registration as to principal or interest, or both. Interest shall be payable at such times as determined by the department and the bonds shall mature at such times and in such amounts as the department prescribes. The department may provide for the retirement of the bonds at any time prior to maturity, and in such manner and upon payment of such premiums as it may determine in the resolution providing for the issuance of the bonds. All such bonds and any coupons attached thereto shall be signed by such officials of the department as the department may direct. Successive issues of such bonds within the limits of the original authorization shall have equal preference with respect to the payment of the principal thereof and the payment of interest thereon. The department may fix different maturity dates, serially or otherwise, for successive issues under any one original authorization. All bonds issued under the provisions of this chapter shall have all the qualities of negotiable instruments under the laws of the state of Iowa. All bonds issued and sold hereunder shall be sold to the highest and best bidder on the basis of sealed proposals received pursuant to a notice specifying the time and place of sale and the amount of bonds to be sold which shall be published at least once not less than seven days prior to the sale in a newspaper published in the state of Iowa and having a general circulation in said state. None of the provisions of chapter 75 shall apply to bonds issued under the provisions of this chapter but such bonds shall be sold upon terms of not less than par plus accrued interest. The department may reject any or all bids received at the public sale and may thereafter sell the bonds at private sale on such terms and conditions as it deems most advantageous to its own interests, but not at a price below that of the best bid received at the advertised sale. The department may enter into contracts and borrow money through the sale of bonds of the same character as those herein authorized, from the United States or any agency thereof, upon such conditions and terms as may be agreed to and the bonds shall be subject to all the provisions of this chapter, except that any bonds issued hereunder to the United States or any agency thereof need not first be offered at public sale. The department may also provide for the private sale of bonds issued under the provisions of this chapter to the state treasurer of Iowa upon such terms and conditions as may be agreed upon, and in such event said bonds need not first be offered at public sale. Temporary or interim bonds, certificates, or receipts, of any denomination, and with or without coupons attached, signed by such official as the department may direct, may be issued and delivered until the definitive bonds are executed and available for delivery.
Iowa Code § 313A.13