Driveways shall have a maximum grade of ten percent (10%) and a minimum width of eighteen feet for a double drive and a minimum width of ten feet for a single drive. Curb cuts for straight curbs and the flare for rolled curbs shall be three feet wider on each side than the driveway pavement. All drive approaches to the sidewalk line or front lot line where no walk is required shall have a concrete or bituminous surface. Because of severe topographic conditions, the Planning Commission shall have the authority to waive the above restrictions on a case by case basis.