4ROAD NARROWS
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These signs may be used with diagram 577, 578, 579, 572, or 575. The symbol is reversed when the road narrows on the left
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May be used only in combination with diagram 576, 577 or 520. A distance, an arrow or both may be added
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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).
| 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).
4.4 Where a road with two lanes in one direction, other than a climbing lane, narrows to a single lane, or a road with a single lane in each direction narrows to a single track, an advance warning sign with the appropriate supplementary plate to diagram 518 or 519 should always be provided. If the sign has to be
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