Traffic Signs Manual/Chapter 4/2013/1
GENERAL
1.1 The Traffic Signs Manual is intended to give advice to traffic authorities and their agents on the correct use of signs and road markings. Mandatory requirements are set out in the current version of the Traffic Signs Regulations and General Directions; nothing in the manual can override these. The advice is given to assist authorities in the discharge of their duties under section 122 of the Road Traffic Regulation Act 1984, but it is for traffic authorities to determine what signing they consider necessary to meet those duties.
1.2 The Traffic Signs Manual is applicable in England, Northern Ireland, Scotland and Wales. References to “the Secretary of State“ should therefore be interpreted as referring to the Secretary of State for Transport, the Department for Regional Development (Northern Ireland), the Scottish Government or the Welsh Government as appropriate.
1.3 Any reference to a "Chapter" is a reference to a Chapter of the Traffic Signs Manual, and any reference to a "section", unless otherwise stated, is a reference to a section in this chapter of the Manual. Where more detailed background information might be helpful, reference is made to Standards and Advice Notes in the Design Manual for Roads and Bridges, available from TSO or www.dft.gov.uk/ha/standards/dmrb.
1.4 Any reference to "the Regulations" or "the Directions" is a reference to the Traffic Signs Regulations and General Directions 2002 applicable to England, Scotland and Wales. Reference to a diagram number or to a Schedule is a reference to a diagram or schedule in those Regulations. In Northern Ireland the relevant legislation is the Traffic Signs Regulations (Northern Ireland) 1997. Diagram and regulation numbering occasionally differs in the Northern Ireland Regulations; this is noted in the text where appropriate. Not all signs referred to in the text are included in the latter Regulations. References to directions are not applicable in Northern Ireland; where these are mentioned, advice should be sought from the Department for Regional Development's Roads Service Headquarters.
1.5 All traffic signs (including road markings) placed on a highway or road to which the public has access must be either prescribed by Regulations or authorised by the Secretary of State for Transport, the Department for Regional Development (Northern Ireland), the Scottish Government or the Welsh Government as appropriate. Care should be taken to ensure that no non-prescribed sign is used unless it has been authorised in writing. Failure to do so may leave an authority open to litigation. Except in the case of certain signs to indicate temporary obstructions or placed by the police in an emergency, signs may be placed only by or with the permission of the traffic authority.
USE OF WARNING SIGNS
1.6 Warning signs are used to alert drivers to potential danger ahead. They indicate a need for special caution by road users and may require a reduction in speed or some other manoeuvre.
1.7 Appropriate warning signs can greatly assist road safety. To be most effective, however, they should be used sparingly. Their frequent use to warn of conditions which are readily apparent tends to bring them into disrepute and detracts from their effectiveness. Unjustified signing should not be used at individual locations simply in response to complaints from the public. Care should be taken to ensure that a route is treated consistently, especially where it crosses the boundary between two traffic authorities.
1.8 Precise dimensions for all diagrams are indicated in the "P" series of working drawings available at www.gov.uk/working-drawings-for-traffic-signs. These also illustrate the permitted variants of symbols and show the correct layout of supplementary plates not illustrated in the Regulations. The "S" series of working drawings provides details of the more complex symbols and pictograms.
1.9 Certain warning signs may be incorporated into directional signs; for further details see Chapter 7.
1.10 Detailed guidance on the use of warning signs at road works is given in Chapter 8.
1.11 To prevent the proliferation of obsolete signs, and unnecessary visual intrusion, direction 37 limits to a maximum of three months the period for which the signs to diagram 790 “NEW LEVEL CROSSING CONTROL AHEAD” and diagram 7014 “NEW ROUNDABOUT AHEAD”, and their variants, may be displayed. See also para 1.43 and section 7.
VEHICLE-ACTIVATED SIGNS
1.12 Regulation 58(7) permits certain warning signs (diagrams 504.1, 505.1, 506.1, 507.1, 510, 512, 512.1, 512.2 and 513) when displayed by means of light-emitting characters or symbols also to display below the sign, and at the same time, the legend "SLOW DOWN" in characters not less than one quarter of the height of the triangle. The signs will be triggered by vehicles exceeding a pre-determined safe speed on the approach to a junction or bend. They should be used only to supplement fixed signing, and not as a substitute for it. Vehicle-activated signs should not be considered until the fixed signing and road markings have been checked to ensure that they comply fully with the guidance in this chapter and in Chapter 5 in terms of correct size, siting, visibility and condition.
SIGN SIZES
1.13 Warning signs are normally prescribed in five sizes. The normal minimum size is indicated in the diagrams, with alternative sizes in brackets. All sizes are in millimetres unless stated otherwise. Signs need to be of a size appropriate to the prevailing traffic speed on the road on which they are used. On roads with a 30 mph speed limit, the smallest prescribed size of warning triangle (normally 600 mm) is usually adequate. On roads where speeds are higher, signs need to be larger. This enables them to be detected at a greater distance and ensures that drivers have sufficient time to recognise and assimilate the warning and take any necessary action before the hazard is met. The largest signs are for use on motorways or high-speed roads. Warning signs which are not appropriate for such roads are not generally prescribed in the largest (1500 mm) size. Appendix A details the appropriate size of sign for various speed ranges, based on the 85th percentile approach speed.
1.14 Where special amenity considerations apply, or there are physical constraints on the width of sign that can be accommodated, the next smaller size can be substituted. It should however be borne in mind that smaller signs are likely to be seen later, and do not become legible until drivers are closer to them, giving less time to react.
1.15 If the accident record suggests that drivers are failing to notice the warning, or seeing it too late to take the necessary action, the next larger size can be used. Conspicuity can also be increased by the use of yellow backing boards (see paras 1.32 to 1.34).
1.16 Many warning signs are accompanied by supplementary plates. Appendix B recommends appropriate x-heights to match the size of the plates to the size of the triangle they are used with, and to ensure adequate legibility. There are restrictions on which plates may be used with individual signs; the plates prescribed for use with each sign are indicated below each diagram illustrated in this chapter. Detailed drawings showing the correct layouts for all permitted variants have been produced by the Department for Transport (see para 1.8).
1.17 A special sign (diagram 7014) is prescribed to warn drivers of a permanent change in the road layout ahead (see also para 1.11). Several variants are prescribed, e.g. "GAP CLOSED AHEAD", "NEW TRAFFIC SIGNALS AHEAD" and "NEW ZEBRA CROSSING AHEAD". The x-height of the sign may vary between 50 and 200 mm (i.e. the capital letter height varies between 70 and 280 mm). The appropriate x-height at a specific site will depend upon the speed of traffic, with the 50 mm x-height suitable for speeds up to 30 mph and 150 or 200 mm for 70 mph. Intermediate sizes should be used for speeds between these extremes.
1.18 The Traffic Signs (Amendment) (No.2) Regulations and General Directions 2011 prescribe a new sign (diagram 7014.1) to be used in the event of either a temporary or permanent reduction in headroom at a bridge. This sign previously required authorisation. The x-height may be between 50 mm and 200 mm, with the same selection criteria as for diagram 7014 (see para 1.17).
1.19 The minimum x-height of the "ANIMAL DISEASE" sign, diagram 574, is determined in a similar manner to diagram 7014 as described in para 1.17, except that the minimum size is 40 mm. This size may be used on narrow rural roads where speeds are low and space is restricted.
SITING
1.20 In general, the greater the speed of approach, the further in advance of the hazard the sign needs to be placed. This is to ensure that drivers have the necessary time to respond to the warning. Appendix A sets out recommendations for the distance from the hazard at which a sign should be sited. If it is impracticable to place a sign within about 10% of the recommended distance, it should be sited further upstream of the hazard at the nearest practicable point. It may be appropriate to supplement it with a distance plate to diagram 572 (see section 18). A sign should not normally be sited more than 10% closer than the recommended distance, as this would be unlikely to provide sufficient warning. Where this is unavoidable, a distance plate should always be used, indicating the distance to the hazard to the nearest 10 yards.
1.21 Warning signs should normally be placed on the left hand side of the road, unless stated otherwise in the text (e.g. hazard markers to diagrams 560 and 561). However, site conditions sometimes make this impracticable. A warning sign might be placed on the right hand side on a left hand bend if it would otherwise be hidden from view, or if there would be no room for it on the left. If a sign is placed on the right hand side of the road, care must be taken to ensure that a driver would not be misled at night or in fog as to which side to pass. It will sometimes be appropriate to duplicate warning signs by providing them on each side of the road, as is recommended at the end of a dual carriageway, or on the approach to a roundabout on a high-speed road.
1.22 It is essential that drivers have an unobstructed view of traffic signs. The distance which should be kept clear of obstructions to the sight line, whether caused by foliage, other signs or street furniture is known as the clear visibility distance. The higher the prevailing traffic speeds, the greater this distance needs to be. It is important therefore that sight lines are properly maintained so that the intended warning is not compromised. Care in siting can minimise future problems of obscuration. Sight lines should not cross private land as it will be difficult to control the growth of vegetation or the placement of other obstructions. It is equally important that warning signs should not be placed where they will obstruct the view of other signs. e.g. advance direction signs. Such problems might be avoided by siting the sign further from the hazard, or on the right hand side of the road.
1.23 Appendix A specifies minimum clear visibility distances. These should normally be measured from the centre of the most disadvantaged driving lane. It is important that the full recommended sight line to the whole of the sign face is preserved. Trimming of foliage only in the immediate vicinity of the sign may not be sufficient; sign visibility should always be checked from the appropriate viewing distance.
MOUNTING
1.24 The normal mounting height measured to the lower edge of a warning sign is between 900 mm and 1500 mm above the carriageway alongside. The greater height should be used where road spray is likely to soil the sign. Where signs are erected above footways, or in areas likely or intended to be used by pedestrians (e.g. pedestrian refuges), a minimum headroom of 2300 mm is recommended, with 2100 mm as an absolute minimum. A clearance of 2300 mm should be maintained over a cycle track or shared cycleway/footway. When supplementary plates are used, the height should be measured to the bottom of the plate.
1.25 Plates should be separated from the sign or another plate by a vertical space not exceeding the x-height of the lettering.
1.26 Except where they support a luminaire, posts should never project above the top of the sign. This practice is unsightly, and needlessly increases visual intrusion and clutter.
MOUNTING MORE THAN ONE SIGN ON A POST
1.27 Research has shown that the greater the number of signs which drivers are presented with simultaneously, the greater the difficulty they are likely to have in assimilating the information. This problem in dealing with information overload increases with age, so that older drivers suffer disproportionately. Generally, therefore, not more than two signs should be mounted on one post. When a sign is accompanied by a supplementary plate, the combination of sign and plate should be regarded as one sign for this purpose. Exceptionally, three signs may be mounted on one post provided none requires a supplementary plate.
1.28 Warning signs should not be mounted on the same post as a STOP or GIVE WAY or terminal speed limit sign, nor mounted on a traffic signal post. When mounted with other types of sign, the triangular warning signs should always be mounted at the top.
1.29 Where two or more warning signs are erected together, the sign relating to the hazard first encountered should be placed uppermost. When a new sign is added to an existing post, it is important to ensure that the correct order is maintained, if necessary adjusting the position of the existing signs.
1.30 Generally no assembly should exceed a height of 4 m above ground level. All proposed assemblies should be critically examined to ensure that the intended warnings are clear. Account should always be taken of the potential environmental impact of tall and cluttered arrays of signs.
1.31 It should also be borne in mind that high-mounted signs may receive little light from vehicle headlamps, particularly on dipped beam. Where such signs are not directly lit but rely on reflectorisation to be seen at night, they are likely to be less legible (see also para 1.36).
BACKING BOARDS
1.32 To improve conspicuity against a complex or dark background, a warning sign may be mounted on a grey or yellow backing board (direction 42). A backing board can also make for a neater assembly, e.g. when a sign requires a supplementary plate, and also eliminates the risk of the plate becoming misaligned. A yellow backing board must be rectangular in shape, but a grey board may be non-rectangular, e.g. to enable a triangular sign to be bracketed off a lighting column (see Chapter 1). A backing board must not itself be provided with a border, nor give the impression of being an additional border. Where it seems that a sign is not being noticed by drivers, it should be checked to ensure that it is well-sited, not obscured by foliage or other obstructions, and is of the appropriate size and in good condition. Only then should the use of a yellow backing board be considered.
1.33 A yellow backing board may be reflectorised to increase its conspicuity at night. This should not usually be necessary on unlit roads, although it might sometimes be helpful on lit roads, particularly where the sign itself is unlit. It may also be fluorescent; this greatly increases conspicuity in dull weather and at dusk. Fluorescence can also be particularly effective in drawing attention to signs mounted in deep shadow, e.g. below overhanging trees. However, fluorescence is visually intrusive and should be used with discretion. The new true yellow materials are less garish than the original yellow-green type and are much to be preferred.
1.34 There are potential disadvantages to the use of backing boards. The larger overall size of the assembly can sometimes obstruct sight lines. A backing board can deprive triangular signs of a primary recognition aid, their distinctive silhouette. Yellow backing boards can be especially environmentally intrusive, and their over-use could eventually devalue their attention-attracting benefits. A less garish way of increasing a sign’s conspicuity is simply to provide a standard sign of larger size. Not only will this be more noticeable than a smaller sign, but it will also improve legibility and hence reading distance, which a yellow backing board cannot. Detailed guidance on the correct design and use of backing boards can be found in Chapter 7 (paras 14.19 to 14.24).
ILLUMINATION
1.35 On unlit roads, reflectorisation generally produces an adequate level of sign luminance in the illumination from a vehicle’s headlamps. In areas of street lighting, however, much higher levels of luminance are required to ensure that signs are always adequately conspicuous. Reflectorised materials cannot guarantee luminance levels comparable to those provided by direct lighting. Modern microprismatic materials achieve high luminances for many drivers in defined situations, but not for all drivers in all circumstances.
1.36 Except in Northern Ireland, the current Regulations therefore require most regulatory and warning signs to be directly lit when sited within 50 metres of a street lamp which forms part of a system of street lighting. In most other circumstances, reflectorisation alone will be satisfactory. However, some signs are sited where they will not receive adequate illumination from headlamps, and it might then be prudent to provide direct lighting regardless of the regulatory requirements. Examples include signs mounted unusually high above the level of the carriageway, or on the off side of the road. Retroreflection is also less effective where the sign is presented at a large angle to the direction of oncoming traffic.
1.37 Illumination requirements are referenced as Item 5 in the tables associated with each diagram illustrated in the Regulations, and the detailed requirements set out in Schedule 17. Most warning signs are required to be illuminated in accordance with Schedule 17 Item 1 or Item 4. Item 4 allows a simple alternative between reflectorisation and direct lighting, wherever the sign is sited. Item 1 signs are required to be directly lit if they are sited within 50 metres of a street lamp forming part of a system of street lighting. However, certain exceptions are permitted in paragraph (4) in column (3) of Item 1. These include road works signs on a road where the permanent speed limit is 40 mph or less and signs marked with an asterisk in column (2), provided they are placed on a single carriageway road which is not a principal or trunk road and has a speed limit of 30 mph or less. Signs that qualify for this exemption from direct lighting need only be reflectorised, although they may be directly lit. It is recommended that high-performance microprismatic retroreflective materials are used where an asterisked sign is reflectorised instead of being directly lit. Materials that offer performance little better than conventional beaded sheetings are unlikely to be adequate.
1.38 All warning signs, including those used at street works and road works must therefore be either reflectorised or directly lit, except for the overhead black and yellow hazard markings and white chord markings used on railway bridges and similar structures, where this is optional. It is recommended that signs that are directly lit are also reflectorised in order to maintain some degree of illumination in the event of failure of the lighting. Where a sign is reflectorised, all parts of the sign face not coloured black must be reflectorised (regulation 19). Partial reflectorisation is unlawful, as is partial lighting.
MAINTENANCE
1.39 Over a period of years, signs gradually become faded and their retroreflective properties diminish. This will reduce both conspicuity and legibility, by day and by night. Excessively discoloured or faded signs (e.g. white backgrounds which have become grey or brown, or red borders faded to pink) and signs where the legend or graphic is peeling cannot be fully effective and need to be replaced. Guidance can be found in TD 25, in Volume 8 of the Design Manual for Roads and Bridges (see para 1.3).
1.40 Signs should be cleaned at intervals appropriate to the site conditions. Signs located where they are subject to heavy soiling from passing traffic, or algae growth (a common problem with signs beneath tree canopies) will need more frequent cleaning. Neglect reduces the external contrast between the sign and its surroundings, making it less likely to be noticed by drivers. It also reduces the internal contrast between legend and sign background, making the sign more difficult to read. Moreover, it seriously reduces light transmission through the retroreflective medium. Dirty signs will be far less effective at night. Older drivers are particularly disadvantaged; the ageing process of the eye means that progressively more light is required to maintain the same legibility performance. Dimmer signs take longer to recognise and to read, reducing the time available for drivers to take appropriate action.
1.41 The importance of maintaining the necessary clear visibility distance is emphasised in paras 1.22 and 1.23. Regular inspection, particularly in summer when the rapid growth of foliage and other vegetation is most likely to cause obscuration, will ensure early detection of any problems.
1.42 A reference number may be placed on the back of a sign in a contrasting colour in characters not exceeding 50mm in height (direction 42(3)). It is unlawful, as well as distracting and unsightly, to place reference numbers on the sign face or on the front of a backing board.
TEMPORARY SIGNS
1.43 Certain signs are intended to be displayed only during transient conditions. These include diagrams 551.1 (Migratory toad crossing), 554 (Flood or No smoking), 554.2 (Ice), 556 (Uneven road), 557 (Slippery road) and some applications of 562 plated with 563 (Other danger). They should be removed when the danger has passed. Many temporary signs are specifically required by the Directions to be removed when the problem they warn of no longer applies, including diagram 574 "ANIMAL DISEASE" and variants of diagram 7010.1 "ROAD AHEAD CLOSED" etc. Diagram 7014 warns of a permanent change in road layout or new traffic signals etc, this sign must be removed within three months of completion of the works (direction 37). Diagram 7014.1 warns of a reduction in headroom at a bridge. Where this reduction is temporary, the sign may be retained only for the duration of the reduction. When a permanent reduction occurs, resulting in headroom of less that 16′– 6″ (5.03 m), the sign may be retained for a period of six months (see para 7.9). Authorities that fail to comply with their statutory responsibilities to remove redundant signs not only devalue the signs but contribute to sign clutter.
1.44 Regulation 53(1)(e) permits a traffic authority to provide a temporary sign to warn of a temporary hazard caused by works being executed on a road, adverse weather conditions or other natural causes, the failure of street lighting or malfunction of or damage to other equipment used in connection with the road, or damage to the road itself. Direction 38 requires such signs to be removed as soon as the hazard has passed, and in any case within six months.
1.45 A sign prescribed in the Regulations must be used where the warning can be conveyed by such a sign. Otherwise it may be designed following the requirements specified in regulation 53. The back of a temporary sign must be grey, black or in a non-reflective metallic finish, as for almost all other signs (direction 42). The use of a yellow or other coloured back is unsightly, visually intrusive and unlawful.