Page:UK Traffic Signs Manual - Chapter 8 - Part 1 (Traffic Safety Measures and Signs for Road). Designs 2009.pdf/163

DUAL CARRIAGEWAY ROADS For the purpose of this paragraph, lightly trafficked means not carrying more than 1200 vehicles per hour per traffic lane left open throughout the period in which the works will be taking place.

For hard shoulder running on two-lane carriageways, one lane should be closed initially and then the remaining lane should be moved to run on the hard shoulder as appropriate. Where a hard shoulder forms part of the running lanes, the number of lanes on the main carriageway should be reduced to match those being diverted prior to the changeover.

Generally, on carriageways with three or more lanes, the initial taper of cones in advance of works should be direct, i.e. if two lanes are being closed it should be by the use of one continuous taper, see Plan DZB7 in Section D6.16. On carriageways with four or more lanes, if flows are very low, then more than two lanes may be closed in one continuous taper. However, if traffic is to run only on the hard shoulder, closing all lanes with a direct taper to allow hard shoulder running is not permissible.

Whilst stepped tapers are not generally recommended, if their use is considered (Plan DZBS, Section D6.16), the designer should take into account the additional length of the traffic management necessary, the extra equipment required, and also time needed for installation and removal. The use of sequential flashing warning lights on the second taper may be beneficial, see paragraph D6.8.6 below.

Consideration shall be given to the use of backlit sequentially flashing warning lights to highlight taper coning in both daylight and darkness. Research has shown that use of these lights can help drivers to identify and make the necessary change of lane much earlier than with conventional warning lights, thereby reducing the risk of taper strikes. The use of these lights shall be restricted to lead-in and intermediate stepped tapers involving a lane drop, and shall not be used when a lane or lanes are narrowed, at a changeover, or a crossover. Where these lights are in use, high intensity flashing lights shall not be used on barriers to diagram 7105 within the taper.

The lights have been authorised for use on the motorway and trunk road network. However, for use on other roads, the need for specific authorisation of these lights should be checked with the relevant Overseeing Organisation prior to their use.

On motorways and dual carriageway trunk roads in with a permanent speed limit of 50mph or more, backlit sequentially flashing warning lights shall be used to highlight both lead-in tapers involving a lane drop and intermediate stepped tapers.

Guide islands should be provided where traffic is to be merged to the left prior to a left lane closure and traffic is transferred to the right-hand lanes, see Plan DZC2 in Section D6.17. Lengths of guide islands excluding tapers are as follows: Where a guide island is to be used and two or more lanes have to be switched to the right to pass a left lane closure, it will be necessary to modify the carriageway markings to ensure that the traffic lanes are continuous at the changeover.

Where a merge-to-the-right layout may be used, for those cases for which relaxations may apply, then the right-hand guide island and modified lane markings may be omitted. In this case, the appropriate lane restriction signs to diagram 7202 variant should be provided. 162