11.—(1) Paragraph (2) applies to the signs shown in diagrams 614, 632, 636, 636.1, 636.2, 637.1, 637.2, 637.3, 638, 638.1 when the arrow is omitted, 639 when the arrow is omitted, 639.1B, 640 when the arrow is omitted, 642, 646, 650.1, 650.2, 650.3, 660, 660.3, 660.4, 660.5, 660.6, 661A, 661.1, 662, 670 (except when displayed on a variable message sign in the manner mentioned in regulation 58(7)(b)), 672, 956, 957, 959, 959.1, 960, 960.1 and 961.
(2) Subject to paragraphs (3) and (4), signs to which this paragraph applies shall be placed at regular intervals along a road which is subject to a restriction, requirement, prohibition or speed limit which can be indicated by the signs.
(3) Signs shown in diagram 670 when varied to “20” need not be placed in accordance with paragraph (2) on a road within an area into which each entrance for vehicular traffic has been indicated by the sign shown in diagram 674.
(4) The sign shown in diagram 670 (except when displayed on a variable message sign in the manner mentioned in regulation 58(7)(b)) shall not be placed along—
(a)a road on which there is provided a system of carriageway lighting furnished by lamps lit by electricity placed not more than 183 metres apart in England and Wales or not more than 185 metres apart in Scotland and which is subject to a speed limit of 30 mph; or
(b)a motorway on which a national speed limit is in force.
(5) The sign shown in diagram 671 shall be placed at regular intervals along the length of a road (other than a motorway) on which—
(a)there is a system of street or carriageway lighting furnished by lamps lit by electricity placed not more than 183 metres apart in England and Wales or not more than 185 metres apart in Scotland; and
(b)a national speed limit is in force.