[With regard to any county which is exempt from the provisions of Section 19-2-3, this section shall read as follows:]
Where bonds have been issued by any road district, separate road district or special road district, and said bonds and interest thereon have been paid and there remains in the sinking fund or maintenance fund of such district any balance of funds collected for the purpose of paying such bonds or interest, the board of supervisors of the county in which such district or districts is located may, in its discretion, transfer any or all of said funds to the county road or bridge fund or any supervisors district road or bridge fund, to be used and expended in working and maintaining the roads of the district for which such bonds were issued, or may, without such transfer, spend such funds for maintenance of roads within the district from which said funds were collected.