The commissioners appointed by such governing body or municipality, or the commissioners whose terms are continued in force as above authorized, shall, subject to the approval of such governing body, have the following authority, powers, and rights: Said commission shall manage and control the affairs of the bridge as a separate proprietary venture, apart from other public roads and bridges within the county, and shall provide for the regular inspection, repair, maintenance, and upkeep of said bridge and its approaches, which expenses and all liabilities which may exist or later come into being or be claimed to exist shall be wholly borne from the bridge properties themselves and the revenues received from the lease of such properties to private or public utilities. In connection with operating the affairs of the said bridge and maintaining the same, said commission is vested with the following powers and authority, subject to the veto power or approval of the governing body owning the said bridge, viz: (1) Contracts and purchases shall be made on the same basis and under the same requirements of advertisement for bids as those made by the board of supervisors; (2) the commissioners may employ a superintendent or manager of the bridge properties and fix the amount of his salary, and either employ or delegate to said manager the employment of subordinate personnel and provide for the wages and compensation of such employees, and, should the commission so determine, may require the manager or other employees to post bond in such sum as the commission may designate for the faithful discharge of their duties as such employees; however, the number of persons employed in an election year shall not exceed the average number employed during the preceding three (3) years, except that additional employees may be hired on a temporary basis in cases of emergency when the specific reasons therefor shall be entered on the minutes of the commission; (3) provide for an adequate bookkeeping system pertinent to the affairs of said bridge and for regular audits, with the revenues derived following the freeing of said bridge to vehicular traffic, if any there be over and above cost of operating and maintaining the said bridge, to be kept by the clerk of the said board or treasurer of the said municipality in a separate account and to so remain, properly invested in the same manner as sinking funds of the county or municipality may be invested, said assets to be subject to bear and discharge the liabilities of the said bridge and not to be utilized for any other or different purpose until a period of at least five (5) years following the freeing of the said bridge from tolls (unless sooner there be another free bridge constructed and opened to public travel crossing said Mississippi River located not more than one (1) mile from said bridge, in which event that factor, rather than the five-year time limit, shall be determinative), and then not until a determination is made by the board or governing authority that such funds, to the extent amassed, will not be further needed for operational maintenance purposes; and that said audits thus caused to be made shall be done by a certified public accountant or accountants duly qualified under the laws of this state; (4) that, without in anywise sacrificing or waiving the entire exempt status of the said bridge properties from ad valorem taxation, to pay a sum or sums in lieu of ad valorem taxes which, by agreement with the taxing authorities of this or any neighboring state, will in no event exceed in any year a sum equaling more than one-half (½) of the average amount paid per year by way of such taxes or in lieu thereof over the five-year period preceding June 15, 1966; (5) employ nationally recognized engineers and such other professional assistance as may be deemed necessary, and to pay reasonable compensation for such services; (6) to have and exercise any other authority and right conferred by existing laws, state or federal, applicable to the operation of such bridge; and (7) fulfill the requirements of any outstanding lease contracts to the extent that the bridge properties will permit and the revenues to be derived from such leases will allow, but without incurring any pecuniary liability on the part of the governing authorities or taxpayers generally.