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T.P.D.M.V.2.4
4*6.7.12 The width of two lane slip roads is based on the need to
maintain two lanes of moving traffic whilst providing sufficient
horizontal clearance between vehicle and parapet. The effective
carriageway width should be 8.75m or 7«75m comprising a 6.75m
carriageway and two marginal strips which should each be 1m wide
on Rural Trunk Roads and 500mm in width on other roads. As with
single lane slip roads the effective width should be maintained
through curves by appropriate widening as shown in Table
4.6*7*2. The desirable minimum standard in this Table is based
on the requirements of a 16.0m articulated vehicle. Absolute
minimum values are also given but these should not normally be
used and in any case not used on bus routes and in situations
with more than the minimum volumes of medium and heavy goods
vehicles. Both desirable minimum and absolute minimum values
include two marginal strips each one metre wide and the
effective width should be correspondingly reduced if 500mm
marginal strips are used,
4.6.7.13 For both two lane and single lane slip roads, where widening is
provided through curves the marginal strips should be maintained
at the same width as those on the approach to the curve.
Table 4.6.7.2
Minimum Effective Carriageway Widths on Slip Hoads
Related to Inside Radius of Curve (m)
Single Lane Slips
{Including Marginal Strips)
Two Lane Slips
(Including Two 1m
Marginal Strips)
Inside
Radius
of Curve
(m)
15
20
25
30
40
50
75
100
150
Straight
6m Effective
Carriageway
Width
5.2m Standard
Effective
Carriageway
Width
Width on Curve
(m)
n/a
n/a
n/a
n/a
8.2
6.8
7.8
6.4
7.2
5.8
6.9
5.6
6.5
5.4
6.3
5.2
6
6
Width on Curve
(m)
5.2
5.2
4.3m Effective
Carriageway
Width
Width on Curve
(m)
7.1
6.2
5.7
5.3
4.7
4.3
4.3
4.3
4.3
4.3
Desirable
Minimum
(m)
n/a
n/a
12.9
12.3
11.3
10.7
10.0
9.6
9.3
8.75
Absolute
Minimum
(m)
n/a
n/a
10.5
10.2
9.9
9.7
9.4
9.3
9.0
8.5