The general assembly may from time to time repeal or reduce any excise or tax pledged pursuant to Section 2i of Article VIII, Ohio Constitution, to the payment of the interest on or principal of the obligations issued pursuant to Section 2i and former section 129.70 of the Revised Code, and may levy any new or increased excise or tax of the state, except ad valorem taxes on real or personal property, income taxes, and fees, excises, or license taxes relating to the registration, operation, or use of vehicles on the public highways, or to fuels used for propelling such vehicles to be available to meet the pledge of the state to such obligations, provided that nothing in this section authorizes any impairment of the obligation of this state to levy and collect sufficient excises and taxes to pay such obligations issued pursuant to Section 2i of Article VIII, Ohio Constitution for which other provision is not made.