Traffic Signs Manual - Chapter 4 - Warning Signs

INTRODUCTION1.5.2.  References to Schedules, Parts, items and paragraphs within TSRGD are shown in anabbreviated format. In this system, “Schedule” is shortened to “S” and “Part” is indicated bythe second number without a prefix. The final element, variously “item” or “paragraph” is alsodenoted by a number without a prefix. This is illustrated in the following examples:1.5.3.  “Schedule 9, Part 6, item 25” becomes “S9-6-25”1.5.4.  “Schedule 11, Part 6, paragraph 3” becomes “S11-6-3”1.5.5.  “Schedule 12, Part 2” becomes “S12-2”1.5.6.  The numbering system contained in the Manual utilises three levels comprising sections,sub-headings and numbered paragraphs. Internal references are in bold blue.1.6 Use of warning signs1.6.1.  Warning signs are used to alert drivers to potential danger ahead. They indicate aneed for special caution by road users and may require a reduction in speed or some othermanoeuvre.1.6.2.  Warning signs can play an important part in improving road safety. However, they shouldonly be used where there is a specific safety issue or hazard, not to sign readily apparentconditions or routine features of the road, such as bends and junctions. Overuse of warningsigns can dilute their effectiveness and tends to bring them into disrepute. For example, itshould not be necessary to place roundabout or traffic signal warning signs in addition to maptype advanced direction signs or where the traffic signals or roundabout are clearly visible.Similarly, junction warning signs should not be necessary in street-lit urban areas, where thereare frequent side-road junctions. Local authorities should work with local communities wherespecific issues and concerns are raised, to make sure the right solution is found. Warning signsshould only be installed where there is an identified hazard or road safety problem, and not tosolely meet a perceived need. Unjustified signing should not be used at individual locationssimply in response to complaints from the public. Care should be taken to ensure that a route istreated consistently, especially where it crosses the boundary between two traffic authorities.1.6.3.  Certain warning signs may be incorporated into directional signs; for further details seeChapter 7.1.6.4.  Detailed guidance on the use of warning signs at road works is given in Chapter 8, andfor the approach to signalled junctions and crossings in Chapter 6.1.6.5.  To prevent the proliferation of obsolete signs, and clutter, Schedule 13 stipulates that thetemporary sign to diagram 7014 “NEW ROUNDABOUT AHEAD” (S13-6-37) and its variants,and the sign to diagram 790 “NEW LEVEL CROSSING AHEAD” (S14-2-67) must only bedisplayed for a maximum period of three months after completion of works. A remove by datemust be placed on the back of the sign. See also 1.15.1 and section 7.1.7 Vehicle-activated signs1.7.1.  S2-7-3 permits certain warning signs (diagrams 504.1, 505.1, 506.1, 507.1, 510, 512,512.1, 512.2, 512.3 and 513) when displayed by means of light-emitting characters or symbolsalso to display below the sign, and at the same time, the legend “SLOW DOWN” in charactersnot less than one quarter of the height of the triangle. The signs will be triggered by vehiclesexceeding a pre-determined safe speed on the approach to a junction or bend. They shouldbe used only to supplement fixed signing, and not as a substitute for it. Vehicle- activatedsigns should not be considered until the fixed signing and road markings have been checked8

INTRODUCTIONto ensure that they comply fully with the guidance in this chapter and in Chapter 5 in terms ofcorrect size, siting, visibility and condition.1.8 Sign sizes1.8.1.  Warning signs are normally prescribed in five sizes. The normal minimum size isindicated in the Schedule diagram by the first dimension, with alternative sizes below. Allsizes are in millimetres unless stated otherwise. Signs need to be of a size appropriate to theprevailing 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. Onroads where speeds are higher, signs need to be larger. This enables them to be detected at agreater distance and ensures that drivers have sufficient time to recognise and assimilate thewarning and take any necessary action before the hazard is met. The largest signs are for useon motorways or high-speed roads. Appendix A details the appropriate size of sign for variousspeed ranges, based on the 85th percentile approach speed.1.8.2.  Where special amenity considerations apply, or there are physical constraints on thewidth of sign that can be accommodated, the next smaller size can be substituted. It shouldhowever be borne in mind that smaller signs are likely to be seen later, and do not becomelegible until drivers are closer to them, giving less time to react.1.8.3.  If the accident record suggests that drivers are failing to notice the warning, or seeing ittoo late to take the necessary action, the next larger size can be used. Conspicuity can also beincreased by the use of yellow backing boards (see 1.12). These are environmentally intrusiveand should only be used sparingly, not as a matter of course.1.8.4.  Many warning signs are accompanied by supplementary plates. Appendix Brecommends appropriate x-heights to match the size of the plates to the size of the triangle theyare used with, and to ensure adequate legibility. There are restrictions on which plates may beused with individual signs and in some cases a plate is mandatory; the plates prescribed for usewith each sign are indicated below each diagram illustrated in this Chapter. Detailed drawingsshowing the correct layouts for all permitted variants have been produced by the Department forTransport (see 1.16.1).1.8.5.  A temporary sign (diagram 7014) is prescribed to warn drivers of a permanent changein the road layout ahead (see 1.6.5). Several variants are prescribed, e.g. “GAP CLOSEDAHEAD”, “NEW TRAFFIC SIGNALS AHEAD” and “NEW ZEBRA CROSSING AHEAD”. Thex-height of the sign may vary between 50 and 200 mm (i.e. the capital letter height variesbetween 70 and 280 mm). The appropriate x-height at a specific site will depend upon thespeed of traffic, with the 50 mm x-height suitable for speeds up to 30 mph and 150 or 200 mmfor 70 mph. Intermediate sizes should be used for speeds between these extremes.1.9 Siting1.9.1.  In general, the greater the speed of approach, the further in advance of the hazard thesign needs to be placed. This is to ensure that drivers have the necessary time to respond tothe warning. Appendix A sets out recommendations for the distance from the hazard at which asign should be sited. If it is impracticable to place a sign within about 10% of the recommendeddistance, it should be sited further upstream of the hazard at the nearest practicable point. Itmay be appropriate to supplement it with a distance plate (see section 17). A sign should notnormally be sited more than 10% closer than the recommended distance, as this would beunlikely to provide sufficient warning. Where this is unavoidable, a distance plate should alwaysbe used, indicating the distance to the hazard to the nearest 10 yards.9

INTRODUCTION1.9.2.  Warning signs should normally be placed on the left hand side of the road, unless statedotherwise in the text (e.g. hazard markers to diagram 560, S2-6-2). However, site conditionssometimes make this impracticable. A warning sign might be placed on the right hand side ona left hand bend if it would otherwise be hidden from view, or if there would be no room for iton the left. If a sign is placed on the right hand side of the road, care must be taken to ensurethat a driver would not be misled at night or in fog as to which side to pass. It might sometimesbe appropriate to duplicate warning signs by providing them on each side of the road, as isrecommended at the end of a dual carriageway, or on the approach to a roundabout on a highspeed road.1.9.3.  It is essential that drivers have an unobstructed view of traffic signs. The distance whichshould be kept clear of obstructions to the sight line, whether caused by foliage, other signs orstreet 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 properlymaintained so that the intended warning is not compromised. Care in siting can minimise futureproblems of obscuration. Sight lines should not cross private land as it will be difficult to controlthe growth of vegetation or the placement of other obstructions. It is equally important thatwarning signs should not be placed where they will obstruct the view of other signs e.g. advancedirection signs. Such problems might be avoided by siting the sign further from the hazard, or onthe right hand side of the road.1.9.4.  Appendix A recommends minimum clear visibility distances. These should normally bemeasured from the centre of the most disadvantaged driving lane. It is important that the fullrecommended sight line to the whole of the sign face is preserved. Trimming of foliage only inthe immediate vicinity of the sign may not be sufficient; sign visibility should always be checkedfrom the appropriate viewing distance.1.10 Mounting1.10.1.  The normal mounting height measured to the lower edge of a warning sign is between900 mm and 1500 mm above the carriageway alongside. The greater height should be usedwhere road spray is likely to soil the sign. Where signs are erected above footways, or in areaslikely or intended to be used by pedestrians (e.g. pedestrian refuges), a minimum headroom of2300 mm is recommended, with 2100 mm as an absolute minimum. A clearance of 2400 mmshould be maintained over a cycle track or shared cycle track/footway. When supplementaryplates are used, the height should be measured to the bottom o

1.1.1. The Traffic Signs Manual (the Manual) offers advice to traffic authorities and their contractors, designers and managing agents in the United Kingdom, on the use of traffic signs and road markings on the highway network. Mandatory requirements are set out in the Traffic Signs Regulations and General Directions 2016 (as amended) (TSRGD).