# The Traffic Signs Regulations and General Directions 2016, Paragraph 6

Extent: E+W+S

(1) The triangle must be legibly and permanently marked with the specification number of the British Standard for an Advance Warning Triangle to indicate a temporary obstruction, namely BS AU47: 1965 or the specification number of a corresponding EEA standard.
(2) The surface coloured red and marked A must be reflectorised.
(3) Not more than 15 square centimetre of the surface marked A may be obscured by constructional components.
(4) The surface coloured red and marked B must be fluorescent.
(5) The surface marked C must be either—
(a) entirely reflectorised; or
(b) a combination of reflectorised and fluorescent.
(6) Not more than 10 square centimetre of the surface marked A may be obscured by constructional components.
(7) Corners of a triangle must be radiused.
(8) All sides of a triangle must be of the same length.
(9) The reflectorised areas of the surface may be internally illuminated provided that such illumination is steady, presents a uniform appearance throughout that area and does not impair the retroreflecting properties of that area of the surface.
(10) The triangle must not be illuminated through external illumination.

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Source: https://www.legislation.gov.uk/uksi/2016/362/schedule/13/part/7/paragraph/6 (the official version)
Page: https://openlegislation.uk/traffic-signs-regulations-and-general-directions-2016/schedule-13/part-7/paragraph-6
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.