39.—(1) The sign shown in diagram 7023 or 7024 may be placed on or near a road only where—
(a)one-way working is necessary along a length of road because part of the width of the carriageway has been temporarily closed to traffic; and
(b)either—
(i)there is no junction with another road along that length; or
(ii)the traffic authority has given express written approval to the placing of the sign in relation to a length of road having a junction with another road.
(2) The sign shown in diagram 543 may be placed in combination with the plate shown in diagram 7030 only on or near a road on which convoy working is in operation and indicated by one or more of the signs shown in diagrams 7025, 7026, 7027, 7028 and 7029.
(3) The sign shown in diagram—
(a)554 when varied to “Flood” or “No smoking”;
(b)554.2 when placed in conjunction with the plate shown in diagram 554.3; or
(c)562 when placed in combination with the plate shown in diagram 563 when indicating “Accident” or when varied to “Census”, “Dust cloud”, “Fallen tree”, “Frost damage”, “Overhead cable repairs”, “Runners in road”, “Smoke” or “Walkers in road”,
may be retained only for so long as the hazard indicated by the sign continues to exist or is expected to recur in the near future.
(4) The sign shown in diagram 633, 636.2 (except when varied to show the name of a traffic authority), 829.1, 829.2, 829.3, 829.4, 829.5 or 1063 may be placed on or near a road only by a constable in uniform or a person acting under the instructions or authority of the chief officer of police.
(5) The sign shown in diagram 829.5 may only be placed on or near a road in an area where police speed checks are from time to time carried out.
(6) The sign shown in diagram 830, 830.1, 830.3, 831 or 832 may be placed on or near a road in connection with a traffic census, if and only if the taking of that census on that road has been approved—
(a)by the traffic authority for the road;
(b)by the chief officer of police of the police area in which the road is situated; and
(c)by or on behalf of the Secretary of State.
(7) The sign shown in diagram 950 may be placed in combination with the plate shown in diagram 950.1—
(a)when the plate is varied to “Cycle event”, only while a cycle rally or similar event is in progress;
(b)in any other case except when the plate is varied to “Cycles crossing”, only while the training or testing of child cyclists is in progress.