Traffic Signs Manual/Chapter 4/2013/3

by Department of Transport (UK)

3DEVIATION OF ROUTE

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BEND SIGNS

These signs may be used with diagram 577, 573.7, 5 73.2, 526 or 575. The symbols may be reversed

May be used with diagram 57 7, 573. 7, 573.2, 526, 570 or 575. The symbol may be reversed

3.1 Diagram 512 should be used to give advance warning of a bend which a driver might find difficult to negotiate without slowing down and the severity of which cannot easily be seen either by day or by night. The symbol should indicate a bend to the left or right as appropriate. The degree of danger at a bend varies mainly with four factors–the speed of approach, the radius of curvature, the superelevation and the skid resistance of the road surface. No uniform objective test can be applied and traffic authorities must rely on a subjective assessment of these factors when deciding whether to use the sign.

3.2 The radius of curvature not only affects the safe speed appropriate to the bend, it might also reduce forward visibility so that drivers need to slow down.

3.3 The sign should be used sparingly and only to indicate a bend hazard. It should not be used simply to allay local apprehension regarding the speed of traffic. Over-use of the sign could eventually compromise its contribution to road safety.

3.4 On high standard all-purpose dual carriageway roads, the signs should be erected in advance of any bend of radius less than 450 metres.

3.5 Edge of carriageway markings may be used with this sign. It might also be appropriate to change the centre line to a warning line. Chapter 5 gives further guidance on the use of these markings.

3.6 Where junctions which warrant signing in accordance with para 2.2 occur on sharp bends, use of diagrams 512.1 or 512.2 avoids the need for separate signs.

3.7 The sign to diagram 513 should be used only where bends of similar severity follow in close proximity. The symbol must be reversed where the first bend is to the right, drivers are likely to be misled if it is in the opposite direction to that indicated. The sign should be used only when the distance between the bends is less than that given in table 3-1. See Appendix A for further guidance on the size and siting of warning signs.

3.8 The distance plate (diagram 570, see section 18) should be used where a series of bends follow each other at distance intervals less than those referred to in the table. Where a double bend sign is used with a distance plate, bends or combinations of bends occurring within the distance shown on the plate should not be signed individually. However, they may be highlighted individually using diagram 515 (see paras 3.13 to 3.19).

Table 3-1

85th percentile speed	Sign size	Distance between bends
(mph)	(mm)	(m)
Up to 30	600	100
31 to 40	750	200
41 to 50	900	250
51 to 60	1200	300
Over 60	1500	350
NOTE: The distance between bends is measured from the end of one bend to the start of the next.

ADVERSE CAMBER

May be used only in combination with diagram 570, 572, 572.7, 572.2 or 573'

Figure 3-1 Risk of lorries overturning on adverse camber
This sign requires authorisation

3.9 Use of the adverse camber plate to diagram 513.1 to supplement a bend warning sign may be appropriate for signing a sharp bend where no superelevation has been applied. The sign may be used in other circumstances where loss of control accidents are attributed to insufficient superelevation, eg a right hand bend on a steep downhill gradient, or when circulating a roundabout. However, over-use will devalue the sign and it should be used only where the problem is likely to be severe.

3.10 Drivers should expect to encounter adverse or insufficient camber on roundabouts. While approach alignment should ideally ensure that vehicles, particularly HGVs, enter the roundabout at a safe speed, this is not always possible. Where there is a problem of large vehicles overturning on the entry to, or circulatory carriageway of, a roundabout, the non-prescribed sign to diagram NP 423 (see figure 3-1) can be considered. The lower panel can be omitted or varied to diagram 513.2. Note that this sign requires special authorisation (see para 1.5). Although this sign includes a pictorial representation of an overturning lorry, it lacks the recognisable red triangle. It should therefore be used only to supplement standard warning signs.

MAXIMUM SPEED ADVISED

May be used only in combination with diagram 5 72, 572. 7, 572.2, 573 or 7009. The speed may be varied

3.11 The advisory speed sign to diagram 513.2 "Maximum speed advised"is prescribed for use only in combination with the "Loose chippings" sign to diagram 7009 (see para 12.4) or the bend warning signs to diagrams 512, 512.1, 512.2 or 513. The sign should be used sparingly, as in general it should be for drivers to judge what speed to adopt. It is not easy to determine a standard safe speed to negotiate a bend; factors which influence this include radius of curvature, camber/superelevation, road surface condition and type of vehicle. The sign may be used where the road layout is such that a driver might be misled, eg at an exit from a high-speed road where significant slowing is required before negotiating a sharp bend. It may also be used on high-speed roads where the horizontal design radius cannot be achieved, but a mandatory speed limit is not imposed. It must not be used with mandatory speed limit signs, nor in place of repeater signs.

3.12 An alternative to diagram 513.2, where drivers tend to enter a bend at excessive speed, is to plate the bend warning sign with diagram 511 "REDUCE SPEED NOW" (see para 2.17).

CHEVRON SIGNS

The number and direction of chevrons may be varied.
May be used with diagram 5 75.2 and when used on the central island of a roundabout must be used with diagram 606'

3.13 The sign to diagram 515 should be used on roundabouts to face traffic on each approach and elsewhere to denote sharp changes in the direction of a road where a "bend" sign alone would not be a sufficient warning. The sign may also be used at a T-junction where the major road turns through 90°. Care should be taken to ensure that a route is signed uniformly, with successive bends of similar severity always treated consistently.

3.14 Because the sign is often mounted in a position where it is especially vulnerable to being struck by a vehicle of which the driver has lost control, supports that will yield easily under impact should be considered (see also para 3.22).

3.15 Chevron signs should never be mounted one immediately above the other, as this produces a confusing zig-zag pattern. They must not be supplemented by diagonal stripes, chequering or other unlawful background markings. Where greater conspicuity is required, perhaps because of the background the sign is viewed against, a yellow backing board may be used. The width of the yellow area should not be less than half the horizontal width of the white chevron. Alternatively, a larger size sign to diagram 515 may be provided. Increasing the size of the chevrons will result in the sign being seen earlier, provided that sufficient sight distance is available. The improved conspicuity and legibility distance might encourage a greater speed reduction.

3.16 The sign is prescribed in heights of 400 mm, 600 mm and 800mm. The smallest size is intended to be used where the 85th percentile speed on the approach to the bend does not exceed 50 mph. The 600 mm size should be used for approach speeds between 51 and 60 mph, and 800 mm where speeds exceed 60 mph. To minimise the potential danger of sharp edges, the corners may be rounded, with a radius not greater than 10mm. When sited adjacent to areas used by pedestrians, the vertical edges of the sign plates should also be protected, e.g. by the use of rectangular posts flush with the edges of the sign.

3.17 A sign should normally comprise a minimum of two chevrons. A series of single chevrons is difficult to install and maintain in alignment and should be used only where there is inadequate space for longer assemblies. On long bends, a greater number of chevrons may be required. Single chevrons are also vulnerable to being turned. This is potentially serious as they might then give a misleading impression to a driver approaching from the opposite direction. This can be avoided by using two posts, or one square post. The shortest prescribed sign is a single module extending from the tip of one chevron to the tip of the next, as illustrated in the diagram.

3.18 Care must be taken when positioning chevrons to ensure that they do not mislead drivers from the opposite direction. Chevrons signs should be placed so that vehicles are required to pass in front of them and not behind. They should never be used in advance of a bend as an alternative to diagram 512.

3.19 The normal mounting height is 1000 mm to the lower edge of the sign, but greater mounting heights may be appropriate to meet particular circumstances, e.g. where a bend is partly hidden over the brow of a hill. When used on the central island of a roundabout, the height should be measured from the kerb level to the centre of the chevron, and the sign must be accompanied by the directional arrow to diagram 606 (direction 20(3)). This may be mounted above, or at the same level as the chevrons but in front of them. In the latter case, at least one complete chevron should be visible on each side.

3.20 These signs may be used on all roundabouts other than mini-roundabouts. In practice it will not be necessary to use them at the very smallest roundabouts, provided the speed limit is 30 mph or less, the diagram 606 arrow being sufficient. They should normally be used whenever the diameter of the central island exceeds 8 metres.

3.21 It the sign is used in the central reserve or on the off side of a slip road on the immediate approach to a roundabout, it should not be sited where it would impair the driver’s view of circulating trafic.

The number and direction of the chevrons and the number of elements making up the sign may be varied

May be used only in combination with diagram 606. May also be used with diagram 5 7 5.2. The number of chevrons and the number of elements may be varied

3.22 Diagrams 515.1 and 515.1A are made from flexible material and designed to recover when struck by a vehicle. In other respects these signs are similar to diagram 515. Their use at particularly vulnerable locations might help to reduce maintenance costs.

3.23 The sign to diagram 515.2 is formed of block paving on the perimeter of a roundabout. It must always be accompanied by a vertical sign to diagram 606 facing each approach, but the paving may be used together with or in place of diagram 515 or 515.1A. This arrangement may be used on any roundabout with a diameter of 4 metres or more. The larger width of chevron (600 mm) should be used when the space between adjacent chevrons is equal to or greater than 1200 mm. In such cases either eleven or thirteen courses should be used. The white blocks must be reflectorised. Authorities considering such installations should take the maintenance implications of dirt and weed control into account.

515.2 Similar to 515 but constructed of block paving May be used only in combination with diagram 606. May also be used with diagram 515 or 515.1A