2.19 Some signs are divided into more than one panel, such as diagram 618.3 illustrated in figure 2-8. The dividing border between each panel has the same width and corner radii as the main sign border. The exception to this is the stack type direction sign which has special design rules (see section 4). The decision to provide more than one panel is based on the need to separate distinct parcels of information.
2.20 The overall size of a sign is determined by the chosen x-height. This will depend on the type of sign and, in most cases, the 85 percentile speed of vehicles using the road. There is a range of standard x-heights from 15 mm (for some waiting restriction time plates not intended to be read from moving vehicles) to 400 mm (for motorway signs). Some signs have specific x-heights prescribed by the Regulations. However, many signs, particularly directional informatory signs, have only minimum and maximum sizes given. In theory any intermediate value could be used, but it is recommended that the main x-height should be to the nearest 5 mm. The table of x-heights for directional signs in Appendix A of Local Transport Note 1/94 lists the standard sizes of 50, 60, 75, 100, 125, 150, 200, 250, 300 and 400 mm. Intermediate x-heights may be used where this would have siting advantages (e.g. spanning a footway) without compromising the target value and legibility of the sign.
ROUNDING OF SIGN SIZES
2.21 With the use of computers in the design and manufacture of traffic sign faces it is not always necessary to round the overall size of a particular sign to "convenient" dimensions. However, where it is considered advantageous to round the size of a sign the following guidelines should be used.
2.22 The amount of rounding is based on the main x-height of the sign. The overall size of the sign shall be rounded up to the nearest me where Z is calculated by taking 5% of the x-height and then rounding up to the nearest 5 mm. Thus for a sign with 150mm x-height, Zwould equal 5% of 150 mm which is 7.5 mm and this would be rounded up to 10mm. The overall size of the sign, in this case, would be rounded up to the nearest 10mm. The table in figure 2-9 gives the value of Z for each standard x-height.
| X—height mm | <100 | 100 | 125 | 150 | 200 | 250 | 300 | 400 |
| Z mm | 5 | 5 | 10 | 10 | 10 | 15 | 15 | 20 |
Figure 2-9 : Rounding of Sign Sizes
2.23 The rounding described in para 2.22 is applied by increasing the space between the sign border and the elements that make up the sign by equal amounts top and bottom, and both sides. Where a sign comprises more than one panel (see para 2.19) the rounding of the vertical dimension may be split equally between each panel or applied to the top and bottom borders only, as for other signs.
2.24 In some cases it may be desirable to round either the vertical or horizontal overall dimension by varying the x-height (see variable x-heights in para 2.20). This method would be appropriate where the sign is being manufactured by computer methods.
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