Traffic Signs Manual Chapter 4 Warning Signs
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| 3.4.4. The sign is prescribed in heights of 400 mm, 600 mm and 800 mm. 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 10 mm. When sited adjacent DEVIATION OF ROUTE 24 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. 3.4.5. The number and direction of the chevrons may be varied. However, 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. 3.4.6. 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. 3.4.7. 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 may be accompanied by the directional arrow to diagram 606 (see Chapter 3). This should be mounted at the same level but in front of the chevrons to reduce clutter, but may be positioned above. At least one complete chevron should be visible on each side. 3.4.8. 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. 3.4.9. If 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 traffic. 3.4.10. Diagram 515 may also be made from flexible material and designed to recover when struck by a vehicle. A yellow border may be added to the outside edge of the part that forms the chevrons. It may include a direction arrow to diagram 606, formed as part of the flexible elements, placed over the chevrons and any yellow border. Its use at particularly vulnerable locations might help to reduce maintenance costs. |