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T*P*D*M.V.2.4
The average gradient through the section and 0.5 km upstream of the merge
is 2% downhill and the predicted heavy vehicle content is 15*. From Table
4*6.8*1 therefore no adjustment is required to the predicted flows.
The total weaving flow is thus 1600 v.p.h.
From Diagram 4,6.10.1 using line B-B (for 80 km design speed and 1400
v.p.h. per lane design flow) the minimum weaving section length Lmin s
240m (N.B. this is taken from the small graph inset which produces a
larger figure than the main graph).
Number of lanes required within weaving section ;«
M - Qnw1 + Qnw2 + Qw1 r. Lmin . Qw2
N . g + C2 x — + 1> —
2200 + 600 + 900 ,*> 240 » 700
* (2 -
H s 3.3 lanes
As the fractional part is small and the weaving flows are not relatively
high it would be advisable in this situation to maintain the dual three
character of the road and provide a three lanes wide weaving section. The
full merging and diverging lane requirements as stated in sections 4.6*8
and 4.6.9 would in any case be provided.
Consider also the situation which is the same in all respect except that
the actual weaving section length is only 600m.
In these circumstances the number of lanes required in the weaving section
would be 3.54. When one considers the lengths of merging and diverging
•lanes required there would be less than 200m between the end of one and
the beginning of the other* In this situation it would generally be more
sensible to run the additional fourth lane throughout the whole section.