In addition to other levies authorized by law, the county commission in counties not adopting an alternative form of government and the proper administrative body in counties adopting an alternative form of government, in their discretion may levy an additional tax, not exceeding thirty-five cents on each one hundred dollars assessed valuation, all of such tax to be collected and turned into the county treasury, where it shall be known and designated as “The Special Road and Bridge Fund” to be used for road and bridge purposes and for no other purpose whatever; except that the term “road and bridge purposes” may include certain storm water control projects off rights of way that are directly related to the construction of roads and bridges, in any county of the first classification without a charter form of government with a population of at least ninety thousand inhabitants but not more than one hundred thousand inhabitants, in any county of the first classification without a charter form of government with a population of at least two hundred thousand inhabitants, in any county of the first classification without a charter form of government and bordered by one county of the first classification and one county of the second classification or in any county of the first classification with a charter form of government and containing part of a city with a population of three hundred thousand or more inhabitants; provided, however, that all that part or portion of such tax which shall arise from and be collected and paid upon any property lying and being within any special road district shall be paid into the county treasury and four-fifths of such part or portion of such tax so arising from and collected and paid upon any property lying and being within any such special road district shall be placed to the credit of such special road district from which it arose and shall be paid out to such special road district upon warrants of the county commission, in favor of the commissioners or treasurer of the district as the case may be; provided further, that the part of such special road and bridge tax arising from and paid upon property not situated in any special road district and the one-fifth part retained in the county treasury may, in the discretion of the county commission and pursuant to a written contract, be shared with any other political subdivision to be used for road and bridge purposes within the county including, but not limited to, constructing, improving, or repairing streets, avenues, or alleys of such political subdivision.