The sign shown in diagram 6002, 6021 or 6031.1 may be displayed only over a traffic lane and the sign shown in diagram 6006, 6006.1, 6006.2, 6008, 6008.1, 6009, 6009.1, 6009.2, 6009.3, 6022 or 6032.1 may be displayed only at the side of the carriageway to which the indications given by the sign relate, or projecting over part of that carriageway, so as to convey warnings, prohibitions or requirements applying to all traffic proceeding along the carriageway in a particular direction.