Tenn. Code Ann. § 54-4-101: Source - Payment - Use

(a) All state moneys appropriated or allotted for the maintenance and improvement of county systems shall be known as county aid funds, to be paid over by the commissioner of finance and administration to the trustees of the several counties in the proportion directed in § 54-4-103 , to be used by the county highway authorities in building or maintaining, or both, county roads and bridges; provided, that any county highway may be taken over and constructed, improved or maintained as a hard surface road by the department of transportation out of its own funds.

(b) Any county has the power and authority by resolution of the governing body of the county, to pledge county aid funds to the punctual payment of principal of and interest on bonds, notes or other evidence of indebtedness issued for the purpose of building, maintaining or improving county roads and bridges, but only after receiving in writing the concurrence of the current superintendent of roads to pledge county aid funds to a bond issue.