Department of Transport

“ Safety fences do not consistently follow the line of the road edge; mounting reflectors on them is likely to mislead drivers as to the true position of the verge. The recommended method of delineating the road edge is to use edge of carriageway markings (incorporating raised ribs if appropriate) together with road studs. It may sometimes be appropriate to use markers on safety fences on sinuous mountain roads over short lengths, or at sharp bends, where separate posts may be inconvenient. ”

“ When mounted on a post specially provided for the purpose, that part of the post which extends above ground level should be not less than 100 mm wide and may be:
(i) of any single colour, or
(ii) coloured black and white in alternate horizontal bands, each band being not less than 225 mm nor more than 350mm deep.
16.3 The black and white banded post enhances the conspicuity of the hazard marker. In rural areas or in areas where speeds are high, this type of post will generally be most suitable. ”