Traffic Signs Manual Chapter 4 Warning Signs
). 1.12 Backing boards
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). 1.12 Backing boards 1.12.1. To improve conspicuity against a complex or dark background, a warning sign may be mounted on a grey or yellow backing board (direction 9). A backing board can also make for a neater assembly, e.g. when a sign requires a supplementary plate, and also eliminates the risk of the plate becoming misaligned. A yellow backing board must be rectangular (including square) in shape, but a grey one may be non‑rectangular. A backing board must not itself be provided with a border, nor give the impression of being an additional border. Where it seems that a sign is not being noticed by drivers, it should be checked to ensure that it is well‑sited, not obscured by foliage or other obstructions, and is of the appropriate size and in good condition. Only then should the use of a yellow backing board be considered. They should be used very sparingly and not as a matter of course. 1.12.2. A yellow backing board may be reflectorised to increase its conspicuity at night. This should not usually be necessary on unlit roads, although it might sometimes be helpful on lit roads, particularly where the sign itself is unlit. It may also be fluorescent; this greatly increases conspicuity in dull weather and at dusk. Fluorescence can also be particularly effective in drawing attention to signs mounted in deep shadow, e.g. below overhanging trees. However, fluorescence is visually intrusive and should be used with discretion. 1.12.3. There are potential disadvantages to the use of backing boards. The larger overall size of the assembly can sometimes obstruct sight lines. A backing board can deprive triangular signs of a primary recognition aid; their distinctive silhouette. Yellow backing boards are environmentally intrusive, and their over‑use could eventually devalue their attention‑attracting benefits. A less garish way of increasing a sign’s conspicuity is simply to provide a standard sign of larger size. Not only will this be more noticeable than a smaller sign, but it will also improve legibility and hence reading distance, which a yellow backing board cannot. Detailed guidance on the correct design and use of backing boards can be found in Chapter 7. tải về 2.25 Mb. Chia sẻ với bạn bè của bạn:
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