Cul-de-sac or dead-end streets designed to be so permanently, shall not be longer than 500 feet and shall be provided at the closed end with a turn-around having an outside roadway diameter of at least 90 feet and a street property line diameter of at least 120 feet. The right-of-way width of the straight portion of the street shall be at least sixty feet. The property line at the intersection of the turn-around and the straight portion of the street shall be rounded at a radius of not less than twenty feet. The location in the center of the turn-around of a planting circle, twenty feet in diameter, curbed all around, having a three-foot wide sidewalk adjacent to the curb all around and planted by the subdivider with trees and/or shrubs of species approved by the Park Development Committee, shall be optional with the subdivider. If a dead-end street is of a temporary nature, a similar turn-around shall be provided and provision made for future extension of the street into adjoining properties.