# Traffic Signs Manual/Chapter 4/2013/4

These signs may be used with diagram 577, 578, 579, 572, or 575. The symbol is reversed when the road narrows on the left
May be used only in combination with diagram 576, 577 or 520. A distance, an arrow or both may be added
May be used only in combination with diagram 576 or 577. A distance, an arrow or both may be added
4.1 Signs to diagrams 516 or 517 should be used where a reduction in width on a single carriageway road presents a hazard. Dual carriageway situations are dealt with in para 4.6. Signs will not normally be needed if the narrowing does not result in the loss of a lane and involves a taper no more severe than indicated in table 4-1. However, signs should be provided regardless of the rate of taper where a lane is lost on a single carriageway road or where the reduction in width is so great that the centre line marking has to be omitted (see also para 4.4). The "REDUCE SPEED NOW" plate (diagram 511) should be used if a significant speed reduction is advisable. These signs must not be used to warn of the termination of a dual carriageway (see diagrams 520 and 521, and paras 5.1 to 5.8).
Table 4-1 Taper criteria for warning sign :
| 85th percentile speed (mph) | Taper |
| Up to 30 | 1 in 40 |
| 31 to 40 | 1 in 60 |
| 41 to 50 | 1 in 80 |
| Over 50 | 1 in 100 |
4.2 The signs may be supplemented by edge lines, hatched markings and hazard markers to diagrams 560 or 561. Diagram 575 "Oncoming vehicles in middle of road" may be used if drivers are likely to be surprised by an oncoming vehicle (see para 19.3).
4.3 The sign to diagram 517 should be used in preference to 516 if the narrowing occurs mainly on one side. Where this is the near side, the symbol is reversed. At the termination of a single carriageway climbing lane, the right hand version is used in advance of the start of the lane loss at the distance specified in Appendix A, and repeated at half this distance. The second sign is not necessary if the 85th percentile speed is below 50 mph. Details of road marking layouts and tapers for climbing lanes can be found in Chapter 5 (paras 5.27 to 5.35) and TD9 in Volume 6 of the Design Manual for Roads and Bridges (see para 1.3).
"with passing places" may be varied to "Use passing places to permit overtaking" or to "No passing places for" and a distance expressed in yards or miles as appropriate
The upper panel may be reversed in a mirror image. The number of ahead arrows may be varied. The distance may be varied (see Appendix C). The lower panel (diagram 876) may be omitted
4.6 The loss of a lane on a dual carriageway road, on a slip road at a grade separated junction or on a one-way street should be indicated using the sign to diagram 872.1. The sign illustrated is for use on a primary route. The background colour is varied to blue when the sign is used on a motorway and to white with black symbols and border when used on a non-primary route.
4.7 The size of diagram 872.1 is determined by the measurement across the arrowhead. A sign is placed on each side of the carriageway, and the pair repeated on roads with higher traffic speeds. Sizes and distances from the start of the taper are detailed in table 42 On motorways and other dual three-lane carriageway roads subject to a 70 mph speed limit, three pairs of signs should normally be provided, at 800, 360 and 180 metres from the start of the taper.
Table 4-2 Size and siting of signs to diagram 872.1 :
| 85th percentile speed | Size of arrow/head | x-height of legend | First signs on approach | First signs on approach | Second signs on approach | Second signs on approach |
| 85th percentile speed | Size of arrow/head | x-height of legend | Distance to start of taper | Legend | Distance to start of taper | Legend |
| (mph) | (mm) | (mm) | (m) | | (m) | |
| Up to 30 | 240 | 120 | 45$^1$ | None | None | None |
| 31 to 40 | 240 | 120 | 135 | 150 yds | None | None |
| 41 to 50 | 320 | 160 | 180 | 200 yds | None | None |
| 51 to 60 | 320 | 160 | 270 | 300 yds | 135 | 150 yds |
| Over 60 | 400 | 200 | 360 | 400 yds | 180 | 200 yds |
| Motorway$^2$ | 400 (480)$^3$ | 200 (240)$^3$ | 800 | ½ mile | 360$^4$ | 400 yds |
NOTES
* On two-lane carriageways subject to a 30 mph speed limit, a single sign mounted on the side of the road on which the lane is to be lost may be adequate, although the possibility of obscuration by parked vehicles should be considered.
* Also all-purpose dual three-lane carriageway roads subject to a 70 mph speed limit.
* Bracketed dimension is used where there are four or more lanes.
* A third pair of signs should be provided at a distance of 180 m indicating a distance of 200 yds.