# The Traffic Signs (Temporary Obstructions) Regulations 1997, Paragraph 1


The areas marked A B and C in the diagram indicate areas of the surface on the face of the triangle as follows:
A—Red reflectorised surface. Not more than a total of 15 square centimetres may be obscured by constructional components.
B—Red fluorescent surface.
C—May have either red reflectorised surface or a combination of both red reflectorised and red fluorescent surface. Not more than 10 square centimetres in each corner may be obscured by constructional components.

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Source: https://www.legislation.gov.uk/uksi/1997/3053/schedule/3/part/1/paragraph/1 (the official version)
Page: https://openlegislation.uk/traffic-signs-temporary-obstructions-regulations-1997/schedule-3/part-1/paragraph-1
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.