Page:UK Traffic Signs Manual - Chapter 8 - Part 1 (Traffic Safety Measures and Signs for Road). Designs 2009.pdf/21

DESIGN CRITERIA marked. The purpose of the inner marking is to indicate the extent of the safety zone and to attract workers' attention when they are in danger of stepping out of it. Suitably supported traffic tape could suffice for this marking; see Part 2: Operations, paragraphs 03.2.11 to 03.2.13. Supports should not be driven into the road surface, but should be stable and able to withstand wind buffeting from passing vehicles. The use of temporary safety barriers is dealt with in Section D3.10.

Adequate working space should be provided around the works to allow for temporary works, stores, the movement of persons, moving parts of plant or machinery such as jibs or booms, equipment and transport. The working space may vary during the period of the works and need not be a constant width around the works. However, the boundaries of the site should be sufficiently visible that workers do not stray into the safety zone or the adjacent live traffic lanes.

Lateral and longitudinal clearances are measured at ground level, but apply above ground up to the headroom dimensions given in paragraph D3.2.23. The lateral clearance is measured horizontally between the edge of the working space and the edge of the carriageway in use by vehicles. It should be noted that the areas within the coned boundaries, including tapers, should be regarded as parts of the safety zone as shown in Figure 3.1.

Designers should bear in mind that excavations or structures very close to the carriageway will tend to cause drivers to shy away from the edge and thus to encroach on another traffic lane. In these circumstances the designer should, where possible, provide additional lateral safety clearance, and ensure the near side traffic lane width is maximised taking all carriageway restraints into account.

For all roads with a permanent speed limit of 50 mph or more, the lateral clearance between the edge of the working space and that part of the carriageway being used by traffic should be not less than 1.2 m.

On single carriageways if the nature of the road is such that a lateral safety clearance of 1.2 m cannot be achieved, then the lateral safety clearance should be as wide as practicable with an absolute minimum of 0.5 m.

Where the lateral safety clearance is less than 1.2 m then a temporary mandatory speed limit of 40 or 30 mph will need to be put in place, using physical safety measures, in association with enforcement of the speed limit where appropriate, to ensure that traffic passing through the site does not exceed the temporary speed limit. These safety measures may include chicanes, temporary speed ramps, traffic control etc. Solely relying on a temporary mandatory speed limit as a safety measure is not deemed sufficient.

On roads other than motorways, if there is insufficient space to provide the minimum lateral safety clearance of 0.5 m, there are a number of available options.


 * If practicable, the road can be closed and traffic diverted along a suitable diversion route (see Section D3.15).


 * If diversion of traffic would be impracticable, traffic speeds must be reduced to below 10 mph and an agreed safe method of working imposed on the site, this must be agreed with the Highway Authority.


 * For short lengths of shuttle working, i.e. 50m or less, on single carriageways, chicanes can be used. At least one chicane is required in each direction of the minimum size to allow a large vehicle to pass through slowly, and traffic must first be brought to a halt by positive traffic control and then released in small batches by careful use of "STOP/GO” signs or manually controlled portable traffic signals. See also Section D5.12. 20