Page:UK Traffic Signs Manual - Chapter 5 Road Markings. 2003 (Sixth Impression 2009).pdf/44



Retroreflective road studs are frequently used to supplement longitudinal road markings. They depend for their brightness on the light from a vehicle's head lamps being reflected back towards the source. The driver sits behind the headlamps and sees a bright reflection from the stud. They are used in addition to reflectorised lines where traffic flows are high, particularly on roads without street lighting. They remain effective in wet weather and also in areas prone to fog, when the efficiency of reflective markings is reduced.

Regulations 31(3) and (7) require white road studs to be used in conjunction with the double white line system (diagrams 1013.1, 1013.3 and 1013.4). They are usually placed in a single row between the lines, but regulation 31(4) permits a double row in certain circumstances (see paras 5.11 and 5.12).

Road studs may be used with most other longitudinal white lines (see direction 31(5), (6) and (7)). They are always used on motorways, and are recommended for use on high speed all-purpose roads, even when street lighting is provided.

For guidance on the use of road studs at the change from dual to single carriageway, see paras 4.58 and 4.59. The positioning of studs relative to edge lines is dealt with in para 4.38.

Bi-directional road studs may be used for certain applications on single carriageway roads, including the double white lines in diagrams 1013.1, 1013.3 and 1013.4 (subject to the exception described in para 5.12), and should always be used in a line that separates opposing flows of traffic. They are not appropriate for marking lines bounding central hatched markings; these should make use of the uni-directional type. This is because bi-directional studs can make the hatched area appear to be another traffic lane, especially on wet roads at night, when the hatched markings may not be clearly visible. Moreover, because reflectors on the leading edge of a bi-directional stud tend to deteriorate faster than those on the trailing edge, it can also result in the studs on the far side of the hatching or taper being brighter than those on the nearer side. There is then a risk of drivers being guided onto the hatched area.

BS 873: Part 4 has been replaced by the European Standard BS EN 1463, and the former type approval process under which studs had to be approved by the Secretary of State has been superseded. Type approval will continue to be needed for studs outside the scope of the European Standard, e.g. those which incorporate a light source. The minimum performance requirement for retroreflective road studs is now specified in direction 57 by reference to the appropriate classes set out in parts 1 and 2 of BS EN 1463.

Studs may be permanent or temporary, and use a glass or plastic reflector, or a plastic reflector with an abrasion resistant protective coating. The standard provides several different photometric performance classes, depending on the stud type.

Studs may also be depressible or non-depressible. In the former, the stud is mounted in a base unit which is embedded into the carriageway. It is designed in such a way that a passing vehicle depresses the stud thus wiping the reflectors clean by a "squeegee" action. Non-depressible studs with rigid retroreflectors can be surface bonded or anchored using suitable adhesives, or embedded into the carriageway using a base unit. The maximum prescribed height for a depressible stud is 25 mm and for a non-depressible stud 20 mm (regulation 32).

Retroreflecting road studs are prescribed for use with reflectors coloured white, red, amber or green (regulation 31(7)). The colours are specified by chromaticity co-ordinates in BS EN 1463-1 and are used as follows: