In addition to the rates authorized in section 11 for county purposes, the county court in the several counties not under township organization, the township board of directors in the counties under township organization, and the proper administrative body in counties adopting an alternative form of government, may levy an additional tax, not exceeding fifty cents on each hundred dollars assessed valuation, all of such tax to be collected and turned in to the county treasury to be used for road and bridge purposes; provided that, before any such county may increase its tax levy for road and bridge purposes above thirty-five cents it must submit such increase to the qualified voters of that county at a general or special election and receive the approval of a majority of the voters voting on such increase. In addition to the above levy for road and bridge purposes, it shall be the duty of the county court, when so authorized by a majority of the qualified electors of any road district, general or special, voting thereon at an election held for such purpose, to make an additional levy of not to exceed thirty-five cents on the hundred dollars assessed valuation on all taxable real and tangible personal property within such district, to be collected in the same manner as state and county taxes, and placed to the credit of the road district authorizing such levy, such election to be called and held in the manner provided by law provided that the general assembly may require by law that the rates authorized herein may be reduced.