Notwithstanding the provisions of § 33.2-340, any town in which 70 percent or more of developable land within its boundaries has a natural grade of 20 percent or more may by ordinance provide for streets or highways established on or after July 1, 1980, with an unrestricted right-of-way width of not less than 40 feet and a hard-surface width of not less than 18 feet, provided that no such requirement of any such town shall be less stringent than that of the county in which the town is located. Streets and highways so established and constructed shall be eligible for payment in accordance with § 33.2-340.