If the amount apportioned to any county from federal aid funds for the purposes mentioned above shall exceed the amount made available to such county from state appropriated funds, then the board of supervisors of such county is hereby authorized and empowered, in its discretion, to use and expend any county road and bridge funds, or any funds available in the general fund of such county, to increase or enlarge the county highway construction program in such county and to match any federal aid funds not matched by state appropriated funds. All such additional funds shall be remitted and turned over by the board of supervisors to the State Treasurer to be deposited in the state highway fund and to be used exclusively in said county on projects on county highways approved by the board of supervisors, the State Highway Commission, and the public roads administration, it being the intention of this section to authorize and empower the board of supervisors of any county to supplement the funds provided for the construction or improvement of projects on secondary or feeder roads in said county out of any funds which the county might have available at the time. For the purpose of providing such supplemental or additional funds, the board of supervisors of any county is hereby authorized and empowered, in its discretion, to issue the road or road and bridge bonds of such county in any lawful amount, said bonds to be issued in all respects in the manner and method, and subject to the restrictions and conditions, now provided by law for the issuance of county road or road and bridge bonds, and shall be payable from the same sources of revenue.