# The Traffic Signs Regulations and General Directions 2016, Paragraph 1

Extent: E+W+S

Where the sign is a variable message sign which displays the numeral by means of light-emitting characters or symbols in such a way that the sign is only visible when associated equipment detects the presence of a vehicle exceeding the speed limit indicated by the sign, the variable message sign may display, beneath the sign displayed on it, the legend “SLOW DOWN” in characters having a height not less than one quarter of the height of the displayed sign.

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Source: https://www.legislation.gov.uk/uksi/2016/362/schedule/10/part/3/paragraph/1 (the official version)
Page: https://openlegislation.uk/traffic-signs-regulations-and-general-directions-2016/schedule-10/part-3/paragraph-1
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.