signs give details of waiting and loading restrictions and the use of on-street parking places. These signs are rectangular and generally mounted parallel to the edge of the carriageway.
1.8 Many regulatory signs are accompanied by supplementary plates. There are restrictions on which plates may be used with individual signs; the plates prescribed for use with each sign are indicated below each diagram illustrated in this chapter. Detailed drawings showing the correct layouts for most permitted variants have been produced by the Department for Transport (see para 1.9).
1.9 Precise dimensions for all diagrams are indicated in the "P" series of working drawings, available free of charge on the Department for Transport's website. These also specify the permitted variants of symbols, and show the correct layout of supplementary plates not illustrated in the Regulations. The "S" series of working drawings provides details of the more complex symbols and pictograms.
1.10 Signs to give advance warning of regulatory restrictions are sometimes needed; most of these are dealt with in [[../../../Chapter 4|Chapter 4]], e.g. STOP and GIVE WAY ahead (diagrams 501, 502 and 503) and mandatory height restriction (diagrams 818.3 and 818.4).
1.11 Some regulatory signs are accompanied by road markings; details of these are in [[../../../Chapter 5/2009|Chapter 5]].
1.12 Certain regulatory signs may be incorporated into directional signs to give advance warning of a restriction (see para 5.3); for design details see Chapter 7. Such additional guidance is purely informatory; the normal regulatory signs must still be provided to make the restriction enforceable.
1.13 Guidance on the use of regulatory signs at road works and temporary situations is given in Chapter 8.
SIGN SIZES
1.14 It is important that signs giving effect to traffic regulation orders, and intended to be read from a moving vehicle, are of sufficient size to enable drivers to recognise them and assimilate the information in time. They therefore need to be of a size appropriate to the prevailing traffic speed on the road on which they are used (see Appendix A). All sign sizes, generally based on the 85th percentile approach speed, are in millimetres unless stated otherwise.
SITING
1.15 It is essential that drivers have an unobstructed view of traffic signs. The distance which should be kept clear of obstructions to the sight line, whether caused by vegetation, other signs or street furniture, is known as the clear visibility distance. The higher the prevailing traffic speeds, the greater this distance needs to be.
| 85th percentile speed of private cars (mph) | Minimum clear visibility distance (metres) |
|---|---|
| Up to 20 | 45 |
| 21 to 30 | 60 |
| 31 to 40 | 60 |
| 41 to 50 | 75 |
| 51 to 60 | 90 |
| Over 60 | 105 (120) |
1.16 Table 1-1 specifies minimum clear visibility distances. These should normally be measured from the centre of the most disadvantaged driving lane. It is important that the full recommended sight line to the whole of the sign face is preserved. Cutting back of vegetation only in the immediate vicinity of the sign might not be sufficient; sign visibility should always be checked from the appropriate viewing distance.
1.17 The bracketed visibility distance of 120 m in table 1-1 is generally for dual carriageway roads and motorways with a 70 mph speed limit, where the bracketed larger size of sign in Appendix A is used.
1.18 Table 1-1 does not apply to speed limit and speed camera signs (see section 14), signs to diagrams 958 and 958.1 (see paras 15.9 and 17.5 respectively), or to time plates that are parallel to the kerb.
1.19 Regulatory signs that indicate the beginning of a restriction or prohibition and to which direction 8 applies have to be placed in accordance with that direction. The requirement is that the signs must be placed on each side of the road or on each side of the appropriate carriageway of a dual carriageway road, except that signs need only be placed on one side if any of the following circumstances apply:
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