Page:UK Traffic Signs Manual - Chapter 4 - Warning Signs. 2013.pdf/17

 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.

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).

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.

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).

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.

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.

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.

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.

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. 16