S.C. Code § 11-29-20
With respect to the issuance of additional state highway bonds pursuant to the provisions of Article 3, Chapter 11, Title 57 of the 1976 Code, which bonds are to be henceforth secured by a pledge of the full faith, credit and taxing power of the State and are to be additionally secured by a pledge of the revenues derived from the "sources of revenue" as such term is defined in subparagraph (a), paragraph (6), Section 13, Article X of the Constitution, the State Treasurer is hereby directed to set aside from the revenues derived from such sources of revenue received in each fiscal year in which the interest on and principal of state highway bonds are due or will become due so much of the revenues derived from such "sources of revenue" as may be necessary in order to pay the interest on and principal of all state highway bonds due and falling due in such fiscal year and the State Treasurer shall thereafter apply such monies to the punctual payment of such principal and interest as the same respectively fall due. In the event that the revenues derived from such sources of revenues so pledged prove insufficient to meet the payments of the interest on principal of such state highway bonds in such fiscal year, then the State Treasurer is authorized and directed to set aside from the general tax revenues received in such fiscal year so much of such general tax revenues as become needed for such purpose and to apply such revenues to the punctual payment of the interest on and principal of all state highway bonds due or to become due in such fiscal year.
S.C. Code § 11-29-20