The state may, to meet casual deficits, or failures in the revenue, contract debts never to exceed in the aggregate one hundred thousand dollars, and no greater indebtedness shall be incurred except for the purpose of repelling invasion, suppressing insurrection, or defending the state in war, and provision shall be made for the payment of the interest annually, as it shall accrue, by a tax levied for the purpose, or from other sources of revenue, which law providing for the payment of such interest by such tax shall be irrepealable until such debt is paid; Provided, that if the Legislature determines by a three-fifths vote of the members elected thereto that (1) the need for construction of highways in this state requires such action, it may authorize the issuance of bonds for such construction, and for the payment of the interest and the retirement of such bonds it may pledge any tolls to be received from such highways or it may irrevocably pledge for the term of the bonds all or a part of any state revenue closely related to the use of such highways, such as motor vehicle fuel taxes or motor vehicle license fees and (2) the construction of water retention and impoundment structures for the purposes of water conservation and management will promote the general welfare of the state, it may authorize the issuance of revenue bonds for such construction, and for the payment of the interest and the retirement of such bonds it may pledge all or any part of any state revenue derived from the use of such structures; and provided further, that the Board of Regents of the University of Nebraska, the Board of Trustees of the Nebraska State Colleges, and the State Board of Education may issue revenue bonds to construct, purchase, or otherwise acquire, extend, add to, remodel, repair, furnish, and equip dormitories, residence halls, single or multiple dwelling units, or other facilities for the housing and boarding of students, single or married, and faculty or other employees, buildings and structures for athletic purposes, student unions or centers, and for the medical care and physical development and activities of students, and buildings or other facilities for parking, which bonds shall be payable solely out of revenue, fees, and other payments derived from the use of the buildings and facilities constructed or acquired, including buildings and facilities heretofore or hereafter constructed or acquired, and paid for out of the proceeds of other issues of revenue bonds, and the revenue, fees, and payments so pledged need not be appropriated by the Legislature, and any such revenue bonds heretofore issued by either of such boards are hereby authorized, ratified, and validated. Bonds for new construction shall be first approved as the Legislature shall provide.