Page:UK Traffic Signs Manual - Chapter 8 - Part 1 (Traffic Safety Measures and Signs for Road). Designs 2009.pdf/167

DUAL CARRIAGEWAY ROADS

Island sites, i.e. sites in which live traffic travelling in the same direction passes on both sides of the works area, must not be used on dual carriageway roads where workers would need to work between lanes of live traffic.

Where it is essential to maintain traffic capacity by opening an extra lane, an island site may sometimes be necessary, but only at times when no work is in progress and the presence of the workforce is not required, e.g. curing concrete etc. In such exceptional cases suitable measures need to be taken to protect the isolated area and to split the traffic.

Where it is necessary to operate on an island site on a dual carriageway road, the approach to the site should be as for the closure of a right-hand lane with traffic split and diverted either side of the closed lane or lanes using a sign to diagram 7234 or 7238, as appropriate, together with suitable coning etc. to guide the traffic into the lanes each side of the island.

At the end of the island site, suitable coning, together with signs to diagram 7231, 7232 or 7239 as appropriate, will be required to ensure that no conflict arises as the traffic joins together.

There should be a presumption that heavy goods vehicles should be prohibited from all but the left-hand lane where there are only two lanes and from all but the near side two left-hand lanes where there are three or more lanes except where:


 * it is expected that the flow of heavy goods vehicles will exceed 850 vehicles per lane per hour, in any hour — flows in excess of this volume cannot be accommodated in single lanes, or
 * an investigation on the relevant section of carriageway shows there is insufficient clearance for heavy goods vehicles under any of the structures in the near side lanes, see paragraph D6.12.3.

A sign incorporating the symbol shown in diagram 7282 should be used where a lane is required to have a weight restriction. Where there is the need to restrict vehicles above a certain width, signs incorporating diagram 7283 or 7283.1 should be used, indicating the appropriate restricted lanes.

Where there is the need to restrict vehicles above a certain height, signs incorporating diagram 7284 or 7284.1 should be used, indicating the appropriate restricted lanes.

Where an entry slip road joins a section of two-lane contra-flow, the limit of 850 heavy goods vehicles per hour may need to be reduced. An individual assessment of each such situation is necessary and the designer shall carry out a detailed risk assessment to demonstrate that all risks have been addressed.

The key issues associated with implementing temporary traffic management on wider carriageways are: 166
 * personnel crossing the carriageway, availability of reliable gantry sign technology,
 * sign obscuration; and
 * sign size and space requirements.