Page:UK Traffic Signs Manual - Chapter 8 - Part 1 (Traffic Safety Measures and Signs for Road). Designs 2009.pdf/72

DESIGN CRITERIA The traffic management designer should consider the risks involved with the introduction of contra­ flow traffic and select an appropriate temporary mandatory speed limit. Where the permanent mandatory maximum speed limit through a tunnel is 60 mph or more, the designer should give consideration to imposing a temporary mandatory maximum speed limit on the approaches and through the tunnel of 40 mph or less, and where the permanent mandatory maximum speed limit is 40 mph or 50 mph, a temporary mandatory maximum speed limit of 30 mph or less should be considered.

The road layout at the transition between single and dual carriageway roads, and vice versa, can vary considerably and therefore particular care is required when designing temporary traffic management for works in the vicinity of this area.

Signing, particularly advance signing, should be based on the speed and nature of the approach road as this generally dictates the maximum speed at which traffic will approach the works. For example, works on a dual carriageway road, but close to an end of a single carriageway section, will reflect the speed characteristics of the single carriageway road. The location and number of approach signs for different types of road is given in Table A1.1 (Appendix 1).

Signing on the single carriageway approach road should include a "road narrows" sign to diagram 517. It is recommended that the "lane closed ahead" sign to diagram 7202 should not be used on a single carriageway two-way road. If used on a road that consists of a single lane in each direction, this sign is likely to confuse drivers and could lead to an error of judgement resulting in a head-on collision.

The start of the dual carriageway section should already be signed on the central reservation with a "keep left" sign to diagram 610 which may have a "Dual carriageway" plate to diagram 608. In addition, consideration should be given to providing "no entry" signs to diagram 616, on the end of the opposing traffic dual carriageway section.

The start of the single carriageway section should already be signed by appropriate signs to diagram 520 or 521.

On a single carriageway road where the works commence between the start of the dual carriageway and 600 m downstream, coning should commence at the start of the dual carriageway, effectively extending the single carriageway along the dual carriageway to direct traffic in single file past the works.

On a single-carriageway road where sightlines are particularly poor, such as on left-hand bends, a duplicate set of signs should be placed on the off side of the carriageway to supplement those on the near side.

If the works are on a single carriageway road just beyond the end of a dual carriageway, the advance signs that are placed on the dual carriageway should relate to those of a single carriageway, that is, the "road narrows" sign to diagram 517, although the number and spacing would relate to the speed of the dual carriageway section. When appropriate, coning should be continued from the end of the dual carriageway road narrowing so that traffic is restricted to a single file past the works and onto the single carriageway beyond.

Where there are road works on, or adjacent to, a short length of dual carriageway between two lengths of single-carriageway road, coning should be used throughout the dual carriageway length to maintain single-file traffic throughout.

Where one carriageway of a dual carriageway road is to be closed and the other used for contra­ flow traffic, it is essential that the signing and coning is appropriate to direct traffic along the carriageway whilst restraining traffic from entering the closed carriageway. The “two-way traffic” sign to diagram 521 should be repeated in both directions along the carriageway, particularly where there are pedestrian and traffic access 71