Traffic Signs Manual/Chapter 5/2009/6
GENERAL
6.1 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.
6.2 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).
6.3 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.
6.4 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.
6.5 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.
TYPE APPROVAL
6.6 BS 873: Part 4 has been replaced by the European Standard BS EN 1463, and the former type approval process under which studs had to be approved by the Secretary of State has been superseded.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.
TYPES OF ROAD STUD
6.7 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.
6.8 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).
COLOUR OF ROAD STUDS
6.9 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:
| WHITE - | to indicate a traffic lane or centre of carriageway marking. |
| RED - | to indicate a line of studs which should not be crossed. It is used mainly to delineate the left hand edge of the running carriageway; studs are omitted at positions where traffic is permitted to cross, e.g. at lay-bys (where green studs are normally substituted). Where studs are used with chevron markings to diagram 1041, 1041.1, 1042 or 1042.1 they must be coloured red on both sides of the marking. |
| AMBER - | to indicate a line of studs which should not be crossed. It is used to indicate the right hand edge of the running carriageway adjacent to the edge of the central reservation or to traffic cones or cylinders at road works, or the marking to diagram 1040.3. Amber studs are also used on the off side of a one-way road (including one-way slip roads and link roads). |
| GREEN - | to indicate a length of the edge of the carriageway which may be crossed. Green studs are used with markings to diagram 1010 (see paras 4.29 and 4.30) at lay-bys and to mark the boundary of acceleration and deceleration lanes on the left hand side of the carriageway. They must not be used in conjunction with Stop or Give Way transverse markings, or with diagram 1009. At lane-drop junctions, and right turnlanes, (see figure 7-7) green studs are used with the marking to diagram 1010 which demarcates the exit lane. |
6.10 On dual carriageway roads, amber studs placed adjacent to the central reservation may have red reflectors on the reverse for use when contra-flow working is needed for road maintenance purposes.
6.11 The colour of the road stud body may be:
(i) white,
(ii) the same as the reflectors or retroreflecting material,
(iii) a natural metallic finish, or
(iv) any other neutral colour (including black).
In the case of studs placed temporarily at road works, the stud body must be fluorescent green / yellow. The use of temporary studs is described in Chapter 8.
STUD SPACING
6.12 The spacing of road studs used with double white lines is dealt with in para #5.115.11. The spacing of studs used with centre lines and lane lines is described in tables 4-1, 4-2 and 4-3, and studs used in conjunction with continuous edge lines or with diagram 1010 in table 4-5 and para 10.11.
6.13 On dual carriageway roads where red, white and amber studs are used, these are normally spaced at 18 m intervals. There may be some minor advantage in offsetting the white lane line studs 9 m longitudinally relative to the red and amber studs. Where red studs are used adjacent to chevron markings, the spacing should be closed up to 3 m centres.
6.14 The standard 18 m spacing should be reduced to 9 m on bends with a radius of curvature less than 450 m, or on roads particularly prone to fog and mist or where there is a severe dazzle problem caused by glare from the headlamps of oncoming vehicles.
ROAD STUDS AT CROSSINGS
6.15 Road studs to diagram 1055.1 or 1055.2 used to mark a crossing place must be coloured white, silver or light grey (regulation 11(4)). They may not be fitted with reflective lenses or with a steady or intermittent light source, but may be formed from retroreflecting material. Although the Regulations permit the use of stainless steel, aluminium, thermoplastic or paint products, some types of metal studs can be slippery when wet, and the potential risk to two-wheeled traffic should be borne in mind. Similar considerations apply to the studs used at other types of pedestrian crossing.
This is NOT an official transcription, and should NOT be considered in any way a controlled copy of the work in question.
This document no longer necessarily represents current practice, as it relates to an earlier version of the regulations (TSGRD 2002 as amended at publication date) rather than the current TSRGD 2016 regulations. It should not be used for actual design or operational use without consulting a more recent edition.
This version was transcribed in May 2015, from a 2009 impression.
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