Page:UK Traffic Signs Manual - Chapter 8 - Part 1 (Traffic Safety Measures and Signs for Road). Designs 2009.pdf/27

DESIGN CRITERIA

The maximum length of a site on a trunk road is 4 km and the minimum distance between sites is as given in Table 3.3 below except where otherwise agreed by the Highway Authority. These requirements may be varied on other roads, with the approval of the Highway Authority. The length of a site is taken as the distance between end of lead taper and the start of the exit taper.

The distance between sites should be measured from the road works end sign to diagrams 7001 and 645, or the road works end signing (7001, 645 and 671) on a yellow background (see paragraph D4.14.4), of the first site to the start of the coning at the second site.

The distance between sites is given in Table 3.3 above and the standard works column should be used where either of the sites is a standard works and the relaxation column where both relate to works with relaxations. In all cases, the given distances between sites may be halved if the traffic demand is not expected to exceed the capacity of the lanes left open to traffic at the second site.

When narrow lanes are used, drivers require a raised level of concentration and this should be taken into consideration when determining the maximum length of the scheme.

Tapers are a fundamental element of traffic management layouts. Their position will be influenced by the location of the works in relation to road features, for example, slip roads, and the need to provide a longitudinal safety zone. However, the prime consideration should be that they are situated where sight lines are good (in both the vertical and horizontal planes). Additional lengths of lane closure may be required for this to be achieved. A taper closing an off side lane should only be positioned at a location where each successive cone is clearly visible to the left of the preceding cone. Similarly for a taper closing a near side lane, each successive cone should be clearly visible to the right of the preceding cone.

The locations of safe taper positions should be identified on all networks and the details recorded. These details should be held by those responsible for maintaining the highway, or their agents, and they shall make them available to those responsible for design and operation of temporary traffic management. 26