Plan DZB8 Lane-change zone for a stepped taper closure on a dual carriageway road for which the national speed limit applies
The principles are:
- when lanes are closed using stepped taper lane closures, the distance between the closures is a minimum of 800 m;
- a second set of wicket signs indicating the closed lane (7202) with distance plate "800 yards" (7208) on the near side and off side, is placed 800 m in advance of the works. These signs are repeated, with the appropriate distance plate, at 200 yard intervals to a point 200 yards in advance of the works, i.e. at 600 m, 400 m and 200 m; and
- on dual carriageway roads of five lanes or more when the works require closure of the near side lane(s), subject to certain flow limits (see paragraph D6.13.11), the wicket signs indicating the closed lane (7202) on the off side of the carriageway may be omitted. Where a temporary mandatory speed limit is in place, one pair of temporary speed limit signs is required, followed by repeater signs:
- the temporary speed limit sign (670), which will generally be 50 mph, is to be placed on the near side and on the central reservation 50 m in advance of the first sign indicating lane closures or restrictions (e.g. signs to diagram 7201, 7202, 7201.1); and
- for a temporary speed limit of 50 mph the distance between successive signs on the same side of the carriageway should not exceed 700 m, with a maximum of 450 m between consecutive repeater signs on alternate sides of the carriageway. For temporary mandatory speed limits of 40 mph or less, see Table 3.4, Note 1.
For entry taper details, including relaxations, see Plan DZB3. Consideration should be given to the use of backlit sequentially flashing warning lights on the tapers to highlight the taper coning and distinguish it from the long straight stretches of coning (see paragraph D3.12.2).
Signing to Detail A is located on the hard shoulder opposite the "keep left/right" sign (610) at the start of the taper and opposite the end of the taper.
For works for which relaxations apply, the size of signs to diagram 7202 in the left-hand side of the carriageway should be as given in Tables A1.1 and A1.2 (Appendix 1) but the signs on the central reservation may be reduced to 1350 mm. The x-height on the supplementary plate to diagram 7208 should be reduced proportionally.
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