# The Traffic Signs Regulations and General Directions 2016, Paragraph 3

Extent: E+W+S

(1) The sign must be a flexible sheet on which a triangle appears and the total area of the sheet, including the red triangle, must be not less than 0.8 square metres.
(2) The triangle must be equilateral.
(3) The area marked A must be reflectorised.
(4) Where the area marked B is coloured white (as shown in the diagram) it must be reflectorised.
(5) The area marked B may be coloured yellow;
(6) Any part of the sign coloured yellow must be fluorescent and may be reflectorised.

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Source: https://www.legislation.gov.uk/uksi/2016/362/schedule/13/part/7/paragraph/3 (the official version)
Page: https://openlegislation.uk/traffic-signs-regulations-and-general-directions-2016/schedule-13/part-7/paragraph-3
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.