Page:UK Traffic Signs Manual - Chapter 5 Road Markings. 2003 (Sixth Impression 2009).pdf/39

 The above procedure achieves the following:

(i) the minimum length for an overtaking stretch is V,

(ii) the minimum length for a broken line element within a system is V, and

(iii) the minimum length for a stretch of warning line between two systems is V / 2.

This minimises both frequent changes of pattern and the length of continuous line put down at places where visibility is adequate.

The use of offset double lines on alternate sections of three-lane roads (other than three-lane hills, see paras 5.27 to 5.32) to facilitate overtaking in the centre lane is not recommended. Drivers will not respect restrictions which have no apparent justification. Carriageways 10 m or more in width may be marked with a centre of carriageway marking in accordance with table 4-3, or with double white lines if there are four or more lanes (see para 5.26).

On single carriageway roads with two or more lanes in each direction, the centre may be marked with a double continuous line irrespective of visibility. This should eliminate the possibility of a vehicle overtaking in one direction being confronted by an opposing vehicle which is "double overtaking" bycrossing the centre line.

A three-lane hill is intended to provide two lanes for ascending traffic so that faster-moving vehicles may overtake slower ones in safety. The downhill traffic may be fully confined to one lane, or partially confined if overtaking is permitted. The left hand uphill lane should be a continuation of the nearside lane, with the widening to the right, so that slower vehicles do not have to change lanes at either end. The procedure for marking three-lane hills, set out below, is designed to result in markings that allow downhill overtaking only at those locations where visibility is extensive in both directions.

A three-lane hill is marked with a lane line (diagram 1005 or 1005.1) separating the two uphill lanes, and a double white line separating them from the downhill lane (see figure 5-6). Where the carriageway width is the standard 10 m (excluding any edge strips) it should be marked so that the uphill climbing lane is 3.2 m wide and the other lanes each 3.4 m wide. For further details see TD 9 / 93 in the Design Manual for Roads and Bridges (Volume 6).

The double white line will always feature a continuous line on the side of the uphill traffic. On the downhill side, where certain criteria are met, the line may be broken to permit overtaking. These criteria are determined as follows:

(i) establish the 85th percentile traffic speed for the downhill direction, and determine from table 5-2 the appropriate warning line visibility distance W,

(ii) measure downhill visibility with the observer on the proposed alignment of the double white line, but with two targets, one on the proposed alignment, and the other on the lane line separating the two uphill lanes. The visibility criteria are satisfied only when both targets are simultaneously visible at a distance W from the observer, and when no part of the sight line to the target on the lane line at any point passes over the inside uphill lane (where it could be obscured by an uphill vehicle). This ensures adequate forward vision for a driver in either direction who intends using the centre lane to overtake,

(iii) a broken line is installed for downhilltraffic only where the criteria in Step 2 of para 5.23 are satisfied, and only if it can be installed for a minimum length W. Otherwise a continuous line is used toprohibit downhill overtaking. 37