All lots shall have a frontage on a public street equal to the minimum lot width specified in the Middletown Zoning Ordinance. With the permission of the Planning Board, a single-family residential lot may have a minimum of fifty (50) feet of frontage on a cul-de-sac provided that the distance from the side lot lines on opposite sides of the lot, as measured at the front yard depth, is no less than one hundred (100) feet.