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T.P.D.M.V.2.4
4.3*11 Left Turning Lanes (Merging)
4*3.11.1 Merging lanes allow left turning minor road traffic to
accelerate before joining the major road traffic. They are
normally only appropriate at dual carriageway junctions where
the design speed of the major road is 80 km/h or above and the
volume of left turning minor road traffic exceeds 600 vehicles
AADT. The flow figure may be reduced to 450 vehicles AADT where
there is an up gradient exceeding 4JC or where the percentage of
heavy goods vehicles exceeds 20%. Merging lanes should never be
used at single carriageway physical island layouts.
4.3*11,2 A separate turning lane, preferably of radius 25m, should be
used to introduce the merging lane from the minor road. The
initial width of the lane, which will depend upon the radius of
the turning lane, should be decreased at a constant taper of 1
in 15* This taper should be introduced relative to the
perpendicular to the minor road centre line at its point of
entry to the major road, not relative to the major road centre
line. A left turn merging lane is shown in Diagram No.
4.3*16.5.