# The Traffic Signs Regulations and General Directions 2016, Paragraph 41

Extent: E+W+S

(1) An audible or tactile warning in the form of a raised rib may be incorporated into the white parts of the marking, in the manner shown at item 12 of the sign table in Part 4 of this Schedule, when the marking is used to delineate the boundary between an emergency refuge area and an actively managed hard shoulder.
(2) Ribs on an individual white mark must be 250 mm apart.

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Source: https://www.legislation.gov.uk/uksi/2016/362/schedule/11/paragraph/41 (the official version)
Page: https://openlegislation.uk/traffic-signs-regulations-and-general-directions-2016/schedule-11/paragraph-41
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.