Page:UK Traffic Signs Manual - Chapter 8 - Part 1 (Traffic Safety Measures and Signs for Road). Designs 2009.pdf/159

 *communication and electricity cables in the central reservation;
 * temporary drainage of the crossover surfacing;
 * reuse for future maintenance;
 * illumination requirements (see paragraph D6.5.4 below and Part 2: Operations, Section O4.8); and
 * arrangements for access to roads and properties within the closed section.

Crossovers should be designed and constructed so that the design speed is consistent with the proposed temporary mandatory speed limit for the works (see TA 92 "Crossover and changeover design" (DMRB 8.46)). In such cases, "keep left/right" signs to diagram 610 and "lane closed" barriers to diagram 7105 should be used behind the coning to mark the crossover.

If the crossover cannot be designed for this proposed speed limit then it should be designed for an appropriate lower design speed limit and the temporary mandatory speed limit should be further reduced locally at the crossover. In this case, the length of the local mandatory speed limit will normally be less than 800 m. This is acceptable in this case as the overall length of speed controlled zone (i.e. the blanket temporary mandatory speed limit) is greater than 800m. In these cases "turn left/right" signs to diagram 606 and "sharp deviation of route" signs to diagram 7104 should be used behind the coning to mark the crossover. See also paragraph D3.7.18.

On unlit roads where horizontal or vertical alignments, or the road surface through the crossover, are below standard, the application of temporary street lighting to the crossover and approach areas should be considered. The lighting of crossovers is dealt with in British Standard BS5489-12:2003. Additional advice is given in Section 5 of TA 92.

The detailed arrangements for crossovers are shown in Section D617 on Plan DZC6 for a singlelane crossover on a two-lane dual carriageway and Plan DZC7 for a two-lane crossover on a three-lane dual carriageway. Plan DZC8 shows the arrangements for a crossover for three narrow lanes.

On completion of the works the crossing should be closed and the safety barrier re-instated. For further advice on safety barriers see TD 19 "Requirement for road restraint systems" (DMRB 2.2.8).

The required crossover lengths may be calculated using Tables 6.1 to 6.4 below, depending on whether survey parameters are known or not. The distances have been calculated from TA 92 and rounded up to the nearest 9 metres for ease of use. Where an off side lane goes into an off side lane, the paved length is equal to the crossover length.

TA 92 uses the concept of design speed for crossovers. This speed is directly related to the temporary mandatory speed limit of the road rather than the permanent speed limit and TA 92 gives details of this relationship. The distances given in Tables 6.1 to 6.4 are given in terms of the temporary mandatory speed limit.

The term "step increase" is used in TA 92. The range of this increase is from 0 to 4 and the greater the step increase the more adverse parameters exist at the site. If the following parameters are known and have the values given, then the 0 step increase lengths in Tables 6.1 to 6.4 may be used. 158
 * worst case resultant camber less than 2.5 %;
 * no change from assisting superelevation to adverse camber through entry or exit curve;
 * crest K value is "desirable";