14.17 Where signs incorporating more than one symbol on the same line are shown on the working drawings (e.g. diagrams 2603, 2606, 2608 and 2701 variant), the symbol sizes shown should not be changed. Similarly, tourist attraction symbols have fixed sizes which should not be changed.
14.18 The horizontal gap between symbols on the same line is generally 2.5sw. However, the appearance of the sign can sometimes be improved by increasing this value to 4sw. There are no fixed rules regarding symbol spacing, except those shown on the working drawings. Where the spacing of particular symbols is not covered by the drawings, designers should use their discretion in deciding whether the horizontal gap should be increased to 4sw. The aim is to ensure that the symbols on the sign in question are clearly discernible as separate entities when viewed from a distance, and avoid a cluttered appearance.
USE OF BACKING BOARDS
14.19 To improve conspicuity against a complex or dark background, a sign may be mounted on either a grey or a yellow backing board (direction 42(5)). This board must not be provided with an additional black border. White backing boards are not permitted. No legend may be applied directly to a backing board. Under no circumstances must striped or chequered backing boards be used. Not only are these unsightly, but they tend to camouflage the sign by breaking up its outline. They are also unlawful. Where a yellow board is used, this should not have the appearance of an additional sign border. The minimum width of any yellow area on a single rectangular sign should therefore be 6sw. In the case of the chevron sign shown in diagram 515, the width of the yellow area should not be less than half the horizontal width of the white chevron. Triangular yellow borders and circular backing boards producing a bullseye effect are not permitted (direction 42(6)).
14.20 Yellow backing boards, particularly if they use fluorescent material, can be very effective in drawing attention to signs mounted in deep shadow, for example below overhanging trees.
14.21 There are, however, potential disadvantages to the use of backing boards. A grey board can deprive triangular and circular signs of a primary recognition aid, their distinctive silhouettes. Yellow backing boards can be environmentally intrusive, and
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