# Traffic Signs Manual/Chapter 4/2013/A

SIZES OF WARNING SIGNS AND SITING DETAILS
| 1 | 2 | 3 | 4 |
| 85th percentile speed of private cars | Height of triangular warning signs $^3$ | Minimum clear visibility distance $^4$ | Distance of sign from hazard $^5$ |
| (mph) | (mm) | (m) | (m) |
| Up to 20 | 600 | 45 | 45 |
| 21 to 30 | 600 | 60 | 45 |
| 31 to 40 | 750 (600) | 60 | 45-110 |
| 41 to 50 | 900 (750)$^1$ | 75 | 110-180 |
| 51 to 60 | 1200 (900)$^1$ | 90 | 180-245 |
| Over 60 | 1200 (1500)$^2$ | 105 (120)$^2$ | 245-305$^2$ |
NOTES
1. The smaller bracketed sizes shown in column 2 should be used only where special amenity considerations or physical constraints apply (see para 1.14). The minimum clear visibility distance specified in column 3 should not be reduced.
The 1500 mm size shown in column 2, and the largest visibility and siting distances in columns 3 and 4, should normally be used where the speed limit is 70 mph on dual three-lane or four-lane motorways or all-purpose roads with hard shoulders. In other circumstances the 1200 mm size should normally be used, with the 105 m minimum clear visibility distance (see paras 1.22 and 1.23) shown in column 3 and the siting distance (see paras 1.20 and 1.21) shown in column 4 (adjusted in accordance with Note 5 below). However, road safety considerations may require a larger size. The Regulations prescribe a 1500 mm size for most warning signs, which may be used on roads other than those described above.
3. The table below shows, in millimetres, the appropriate heights of the triangular warning signs and the diameters of regulatory signs that indicate the headroom of a bridge or other structure. For signs on the approach, the minimum clear visibility distance and the distance from the hazard shall be in accordance with the above table for all warning signs. The signs to diagram 530 and 530A when placed on the approach to a hazard are more likely to indicate an overhanging building or structure where the maximum size is 900 mm and 1200 mm respectively (see Appendix B) rather than to indicate a low bridge (see section 7).
| Diagram number and sign location | 85th percentile speed of private cars (mph) | 85th percentile speed of private cars (mph) | 85th percentile speed of private cars (mph) | 85th percentile speed of private cars (mph) |
| Diagram number and sign location | 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.
​6. The combined metric/imperial height restriction warning triangle (diagram 530A) incorporated into a directional sign or the sign to diagram 818.5 (see figure 7-3 in this chapter and Appendix D in Chapter 7) is 30 stroke widths in height. The combined metric/imperial height restriction roundel (diagram 6292A) incorporated into a directional sign or a sign to diagram 818.3 or 818.4 (see figure 7-2 in this chapter and Appendix D in Chapter 7) is 30 stroke widths in diameter. The table below sets out recommended x-heights and corresponding triangle heights and roundel diameters for the signs to diagrams 818.3, 818.4 and 818.5, appropriate to various 85th percentile speeds. The dimensions in brackets apply where motorways and all-purpose dual carriageway roads have three or more lanes per carriageway. For appropriate x-heights for directional signs, see Appendix A in Local Transport Note 1/94, available from TSO or www.gov.uk/government/ publications/local-transport-notes.
| 85th percentile speed of private cars | x-height | Triangle height/roundel diameter |
| (mph) | (mm) | (mm) |
| Up to 20 | 0060 | 0450 |
| 21 to 30 | 0080 | 0600 |
| 31 to 40 | 0100 | 0750 |
| 41 to 50 | 0120 | 0900 |
| 51 to 60 | 0160 | 1200 |
| 61 to 70 | 0200 | 1500 |
| 70 mph speed limit | 240 (300) | 1800 (2250) |
7. 85th percentile speed measurement is dealt with in TA22 "Vehicle speed measurement on all-purpose roads" in Volume 5 of the Design Manual for Roads and Bridges (see para 1.3). The dry weather spot speed should be used.