Traffic Signs Manual/Chapter 5/2009/1

1INTRODUCTION

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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 Executive or the Welsh Assembly Government as appropriate.

1.3 This chapter of the manual describes the design and use of road markings (including road studs), i.e. markings on the surface of the road for the control, warning, guidance or information of road users. Some markings may be used to supplement upright signs; others are intended to be used alone.

1.4 Any reference to a “Chapter” is a reference to a Chapter of the Traffic Signs Manual, e.g. Chapter 3 for regulatory signs or Chapter 4 for warning signs 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 Departmental Standards and Advice Notes. These can be found in the Design Manual for Roads and Bridges, published by the Stationery Office.

1.5 Any reference to "the Regulations" or "the Directions" is a reference to the Traffic Signs Regulations and General Directions 2002 and applicable to England, Scotland and Wales. Reference to a "diagram number" is a reference to a diagram 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 (see Appendix A). References to Directions are not applicable in Northern Ireland; where these are referred to, advice should be sought from the Department for Regional Development's Roads Service Headquarters.

USE OF ROAD MARKINGS

1.6 Road markings serve a very important function in conveying to road users information and requirements which might not be possible using upright signs. They have the advantage that they can often be seen when a verge-mounted sign is obscured, and, unlike such signs, they can provide a continuing message.

1.7 Road markings have their limitations. They may be completely obliterated by snow. Their conspicuity is impaired when wet or dirty, and their effective life is reduced if they are subjected to heavy trafficking.

1.8 Nevertheless, road markings make a vital contribution to safety, e.g. by clearly defining the path to be followed through hazards, by separating conflicting movements and by delineating the road edge on unlit roads at night. They can also help to improve junction capacity, and make best use of available road space. In particular, widespread use of lane markings is desirable; by encouraging lane discipline they improve the safety and efficiency of traffic flow. Longitudinal lines should be designed to ensure a flowing alignment, avoiding sudden changes of direction or sharp tapers of inadequate length. Road marking layout should always be considered in detail at the design stage of any scheme.

1.9 Because of the oblique angle at which they are viewed, road markings appear heavily foreshortened. This effect is countered in the case of worded markings, e.g. SLOW, by elongating the legend (see paras 22.47 to 22.49). Two sizes are prescribed; the larger marking is legible at a greater distance and is used where traffic speeds are higher. Similarly, longitudinal lines need to be wider and longer where speeds are high, in order to maintain adequate conspicuity.

VISIBILITY

1.10 For road markings to be effective, they must be clearly visible both by day and by night. Markings have two principal functions. The first is symbolic, e.g. hatched markings; the driver needs to have learned that these indicate an area which is not available to traffic. The second is guidance; centrelines, edge lines and lane lines help drivers to maintain their lateral position on the road. Some markings, e.g. hazard lines and double white line systems have both symbolic and guidance functions.

1.11 The guidance function is less critical (although still important) in daylight or on lit roads because there are many visual cues available to enable the driver to judge course and position. On unlit roads at night, conditions are very different; the visual stimuli in the distance and to the sides of the road are largely absent. Road markings then become the most important aid in enabling the driver to follow the road.

1.12 Recent collaborative European research has shown that drivers need to be able to detect guidance markings at a distance equivalent to a minimum of two seconds of travel time. If the visibility is less than this, drivers tend to adjust too late when the road changes direction. They run too close to the centre line on left hand bends, or too close to the road edge on right hand bends. The higher the prevailing traffic speed, the greater the visibility distance required to maintain this two-second "preview time". If it is not provided, drivers tend to miss the curve, or proceed in a series of staggers.

1.13 A variety of factors influence the visibility distance of a road marking. It is increased when a line is wider, has a higher mark-to-gap ratio or has a higher coefficient of retroreflected luminance (in the day time, higher contrast with the road surface). Visibility distance is adversely affected by glare from oncoming vehicles, dirty headlamps or windscreen and especially by rain; the glass beads which produce the night time luminance are drowned by excess water, greatly reducing the brightness of the line. Older drivers also see a marking less well than the young; someone seventy years old may suffer a reduction in visibility distance of more than 20% compared with drivers still in their twenties.

1.14 The marking regime prescribed in the UK generally gives adequate levels of guidance in good conditions, i.e. where the road is dry, the driver is young, the vehicle has clean, powerful headlamps and there is no glare from oncoming vehicles. On roads with high traffic speeds, wider lines should normally be adopted where alternatives are prescribed. However, it is important that guidance markings are well maintained. Severe wear reduces both effective width and retroreflective performance, and hence the visibility distance. Further guidance on the maintenance of road markings can be found in paras 23.21 to 23.26.

REFLECTORISATION

1.15 Tiny glass beads are incorporated in road markings so that they reflect the light from vehicle headlamps back towards the driver. This makes the marking much brighter at night than non-reflectorised materials. The new European Standard for road markings (BS EN 1436) specifies several different classes for night-time brightness. Brighter markings are visible at greater distances, and may provide an acceptable level of performance for a longer time before renewal becomes necessary (see paras 23.9,23.10 and 3.16 for further details).

1.16 Markings which maintain night-time performance even when wet may also be specified. This is usually achieved by the use of larger glass beads, but the wet performance of certain road markings may also be enhanced by the use of raised profiles (see paras 4.39 to 4.48, and 23.16).

DIMENSIONS

1.17 Dimensions on the figures are in millimetres unless stated otherwise. Many markings are fully dimensioned in the Regulations. Detailed drawings of the more complex ones are published by the Stationery Office in the series "Working Drawings for Traffic Sign Design and Manufacture" and also on the Department's website.

This work has been mirrored or sourced from material provided on the UK Government website at https://www.gov.uk/government/publications/traffic-signs-manual, which states material is available under the terms of the Open Government License unless indicated otherwise. (Crown copyright acknowledged.)

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.