# Traffic Signs Manual/Chapter 4/2013/5

TWO-WAY TRAFFIC
May be used With diagram 577 578 or 572
5.1 The signs to diagrams 520 and 521 indicate the resumption of two-way traffic on a single carriageway road after a length of dual carriageway and, in the case of diagram 521, after a one-way road. The sign to diagram 522 indicates a two-way road crossing ahead (see para 5.4).
END OF ONE-WAY ROAD
May be used with diagram 570 or 572
May be used with diagram 572
END OF DUAL CARRIAGEWAY
5.5 The road markings required where a dual carriageway road reduces to a single carriageway are detailed in Chapter 5. Table 5-1 below lists the appropriate tapers. Figure 5-1 illustrates the signs and markings needed in a built-up area where speeds are relatively low. The sign to diagram 520 should be Table 5.1 sited in advance of the end of the dual carriageway at the usual distance appropriate to warning signs (see Appendix A). The sign to diagram 521 should be (mph) erected at or as near as possible to the beginning of two-way working, and may be repeated after 100 metres.
| 85th percentile Speed (mph) | Taper |
| Up to 40 | 1 in 40 |
| 41 to 50 | 1 in 45 |
| 51 to 60 | 1 in 50 |
| Over 60 | 1 in 55 |
5.6 Where traffic speeds are high, as on inter-urban roads, more comprehensive signing as in figure 5-2 should be provided.
Figure 5-1 Signing an urban dual carriageway road
Figure 5-2 Signing the end of a rural dual carriageway road
​5.7 Where a high-speed dual carriageway road ends at a roundabout, signs to diagram 520 should be erected on both sides of the carriageway approximately 100 metres before the roundabout. A sign to diagram 521 should be erected approximately 50 metres after the roundabout. Warning signs to diagram 510 should also be used as appropriate (see paras 2.13 to 2.15).
5.8 Where speeds on the dual carriageway road are high, but the length of dualling is so short that it would not be possible to site the signs in accordance with figure 5-2, they may be sited at not less than one half the normal distance from the end of the central reservation, provided they are still duplicated on the right hand side of the carriageway.
The distance may be reduced
The distance "½" may be varied to "¼"
5.9 On a single carriageway road which widens to a dual carriageway for a length of at least 400 metres, an advance sign to diagram 818 should be provided. Siting distances, normally measured back from the nose of the central hatch marking at the start of the dual carriageway, are similar to those indicated in Appendix A for warning triangles. If the dual carriageway is shorter than 400 metres, no advance sign should be provided. The sign to diagram 818.1A may be used to warn drivers that a dualled length is short and so might not be long enough to permit overtaking. The sign may display distances of "¼ mile" or "½ mile" only.
5.10 Further advance warning up to a distance of two miles may also be given by a sign to diagram 818.1. This sign may be used to encourage drivers to delay overtaking until the dual carriageway is reached. Distances greater than two miles are not permitted, as this might result in impatient drivers trying to overtake on an unsuitable length of road.
5.11 For guidance on the appropriate x-height for these signs, see table 5-2.
Table 5-2 Size of dual carriageway signs :
| 85th percentile speed (mph) | x-height (see note) (mm) |
| Up to 30 | 75 |
| 31 to 40 | 100 |
| 41 to 50 | 125 |
| Over 50 | 150 (200) |
NOTE: The larger size shown in brackets may be used on high standard single carriageway roads where speeds are high (e.g. on 10m wide carriageways).
​ROUNDABOUTS ON DUAL CARRIAGEWAYS
5.13 A plain bollard should be used on the central reservation of a dual carriageway or on the splitter island of any other road leaving a roundabout. A bollard may be dispensed with where a directly-lit direction sign is provided in such a position. If the physical layout does not adequately deter traffic from turning into the wrong carriageway or slip road in such situations, direction 7(3) permits "no entry" signs to diagram 616 accompanied by NO ENTRY markings on the carriageway (diagram 1046) to be used without the need for a traffic order, subject to the prior approval of the Secretary of State (see para 1.2). Further guidance on the signing of roundabouts may be found in paras 2.13 to 2.19, 3.13, 3.19 to 3.23 and 5.7.
GAP CLOSURES
A distance in yards to the nearest ten yards may be added before or substituted for "AHEAD"
SIDE ROADS
5.15 Where a minor road crosses or joins a dual carriageway, GIVE WAY or STOP signs (see Chapter 3) should normally be provided on the minor road, supplemented by a "Dual carriageway" plate to diagram 608 (see para 2.1). Where advance warning is needed, signs to diagram 501 supplemented by the plates 502 or 503 as appropriate should be erected in accordance with table 2-1. The "Dual carriageway" plate may be provided below these signs also.
5.16 Special care is needed in signing minor road junctions with dual carriageway roads if the carriageways are separated by a very wide central reservation and the further carriageway could be mistaken for a separate road or cannot easily be seen by a driver on the minor road. In such cases, as an additional safeguard, NO ENTRY (diagram 1046) should be marked on the nearer carriageway to prevent drivers from turning right into it. It may also be appropriate to erect "no entry" signs (diagram 616) on each side of the nearer carriageway, angled so as to be seen by a driver attempting a right turn. Prior approval must be obtained in writing from the Secretary of State before using these signs and markings in such circumstances (see para 5.13). If the layout is not self-evident, a map-type sign on the minor road approach might be helpful.
5.17 On a side road which joins a dual carriageway road where there is no gap in the central reservation, a "turn left ahead" sign (diagram 609) together with a "Dual carriageway" plate (diagram 608) should be used. A "turn left" sign (diagram 606) with a "Dual carriageway" plate should be erected on the central reservation opposite the side road (see figure 5-1).