| Diagram number and sign location |
85th percentile speed of private cars (mph) | |||
|---|---|---|---|---|
| Up to 30 | 31 to 40 | 41 to 50 | Over 50 | |
| 530 mounted on structure | 750 | 900 | 1200 | 1500 |
| 530 on approach | 600 | 750 | 900 | 1200 |
| 530A mounted on structure | 900 | 1200 | 1500 | 1800 |
| 530A on approach | 750 | 900 | 1200 | 1500 |
| 531.1 on approach | 750 | 900 | 1200 | 1500 |
| 532.2 | 750 | 900 | 1200 | 1500 |
| 532.2A | 900 | 1200 | 1500 | 1800 |
| 532.3 (centre of arch) | 750 | 900 | 1200 | 1500 |
| 532.3 (side of arch) | 600 | 750 | 900 | 1200 |
| 532.3A (centre of arch) | 900 | 1200 | 1500 | 1800 |
| 532.3A (side of arch) | 750 | 900 | 1200 | 1500 |
| 629.2 mounted on structure | 600 | 750 | 900 | 1200 |
| 629.2 on approach | 600 | 750 | 900 | 1200 |
| 6292A mounted on structure | 750 | 900 | 1200 | 1500 |
| 6292A on approach | 750 | 900 | 1200 | 1500 |
4. For further guidance on clear visibility distance, see paras 1.22 and 1.23. Siting also needs to take account of the location of other signs (eg. advance direction signs) to ensure that one sign does not obstruct the sight line to another. Provision of a new sign might sometimes require the relocation of an existing one.
5. For further guidance on sign siting, see paras 1.20 and 1.21. Where a range is quoted for siting distance in column 4, progressively larger figures should be used for 85th percentile speeds towards the higher end of the speed range, to compensate for the greater braking distance. Braking distance will also be affected by gradients, and siting distances may need to be increased on steep hills, eg an increase of 50% might be made for a 10% descent. Special considerations apply to the signs listed below:
(i) When used on single carriageway roads:
Diagram 517 "Road narrows" at the end of a climbing lane – see para 4.3
Diagram 563, when indicating "Blind summit" or "Hidden dip", might need to be placed further from the hazard than shown in column 4 of the first table to allow for a hidden vehicle approaching at speed
(ii) When used on high-speed dual carriageway roads:
Diagram 510 “Roundabout ahead” – see para 2.14
Diagram 520 “Dual carriageway ends ahead” – see paras 5.1 to 5.8
Diagram 521 “Two-way traffic” – see paras 5.1 to 5.8
(iii) When used on any road:
Diagram 522 “Two-way traffic on route crossing ahead” – see para 5.4
Diagram 558 "Low-flying aircraft" – see para 14.2.
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