Traffic Signs Manual/Chapter 4/2013/4

by Department of Transport (UK)

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

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).

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 sited at a distance from the hazard significantly different from that recommended in Appendix A, a distance may be added in accordance with Schedule 16 item 6 (see Appendix C). An indication of the distance over which the restriction extends may be given, e.g. "Single file traffic for 400 yds". If the road indicated is a side road, an arrow may be added, pointing horizontally to the left or to the right. Details are shown on the working drawings (see para 1.8).

"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

4.5 If a road is wide enough for only one line of vehicles but there are passing places marked with diagram 822 "PASSING PLACE", diagram 821 "Single track road with passing places" should be used at each end of the single track section. The legend "with passing places" may be varied to "No passing places for" and a distance in yards or miles.

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.

4.8 Guidance on the associated road markings where the number of lanes is reduced on a high-speed road can be found in Chapter 5 (para 4.53).

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		Second signs on approach
			Distance to start of taper	Legend	Distance to start of taper	Legend
(mph)	(mm)	(mm)	(m)		(m)
Up to 30	240	120	451	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
Motorway2	400 (480)3	200 (240)3	800	½ mile	3604	400 yds

NOTES

1. 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.
2. Also all-purpose dual three-lane carriageway roads subject to a 70 mph speed limit.
3. Bracketed dimension is used where there are four or more lanes.
4. A third pair of signs should be provided at a distance of 180 m indicating a distance of 200 yds.