In this district, a loading and access area shall be provided to the rear or side of all commercial buildings. This area shall be sufficiently large so that any vehicle, while servicing such commercial building, shall not protrude out into any street or sidewalk and this area, in all cases, shall be at least 20 feet in depth. The purposes of this area, inter alia, shall be to grant rear or side access to the building for fire and police protection and for the loading and unloading of merchandise and to protect such property and the occupants thereof.