Traffic Signs Manual/Chapter 4/2013/16
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The signs may be coloured red, white or amber and the surface of the sign to diagram 561 may be curved
16.1 Hazard markers (diagrams 560 and 561) may be circular or rectangular in shape, to the dimensions shown. They are prescribed in three colours. As viewed by the drivers of approaching vehicles these are:
(i) red on the left hand edge of the carriageway
(ii) white on the right hand edge of a single carriageway road
(iii) amber on the right hand edge of a dual carriageway road adjacent to the central reservation, or a road carrying traffic in one direction only.
16.2 The top of the sign must be not less than 550 mm nor more than 1000 mm above the surface of the adjacent carriageway (direction 44). 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. In urban areas, or traffic-calmed zones, single-coloured posts may be appropriate.
16.4 The markers may be used to indicate the edge of the carriageway on embankments, mountain roads and other points where special danger exists. They may also be used, supplemented where appropriate with signs to diagrams 516 or 517 (see paras 4.1 to 4.4) to indicate a place where the carriageway suddenly narrows or to indicate obstructions such as a bridge parapet, abutment or building unusually near the carriageway edge. In these cases the markers may be fixed directly to the structure instead of to a separate post, but see also diagram 528.1 (para 7.2).
16.5 The signs must not be illuminated by means of internal or external lighting. They must be reflectorised by one of the means specified in regulation 21 (regulation 19 in the Traffic Signs Regulations (Northern Ireland) 1997).
16.6 Care should be taken to ensure that hazard markers do not appear confusing at night. This may occur for example if headlights (with raised or dipped beams) are reflected from markers delineating more than one bend. It is recommended that, following installation, they are checked at night from a moving vehicle.
16.7 The use of hazard markers on safety fencesor barriers is not recommended on high-speed roads. 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 used in this way, the markers must still conform to the Regulations and to the requirements specified in direction 44 with respect to colour, size, shape and mounting height. Consideration should also be given to the potential consequences of the fence being struck by a vehicle. If the markers are of heavy construction, they could themselves be hazardous.