Notwithstanding the provisions of § 33.2-701 or 33.2-706, the governing body of any county under the urban county executive form of government may expend funds on minor improvements and maintenance of highways not within the secondary state highway system, provided such highways are open for public use. A highway shall be determined to be open for public use by applying the same standards set forth in § 33.2-105 or by final order of a court of competent jurisdiction on or before January 1, 1978, except that in order to be eligible for funds under this section such highways need not be 30 feet wide but shall not be less than 15 feet wide. The maximum amount of mileage to be maintained under this section shall not exceed 30 miles.