TII Publications
DN-GEO-03060
Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade
separated and compact grade separated junctions)
April 2017
Page 50
Figure 5.19: Design of Corner Radii for Rural Simple Junctions, Ghost Island Junctions & Simple
Staggered Junctions
5.6.6
Carriageway Widths
A minimum 0.5 metre hard strip shall be provided throughout all junction layouts, corner radii and
associated tapers.
5.6.7
Through Lanes
At ghost island junctions on single carriageways, the through lane in each direction shall not be greater
than 3.65m wide, exclusive of hard strips, but shall not be less than 3.0m wide on rural roads.
5.6.8
Layout at Left In/ Left out Priority Junctions
For Left In / Left out priority junctions, the layout shall be as shown in Figure 5.20. The left turn only
traffic deflection islands should be set back 0.6m from the back of the hard shoulder or hard strip.
TII Publications
DN-GEO-03060
Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade
separated and compact grade separated junctions)
April 2017
Page 53
Figure 5.22: Skew Junctions
5.6.10
Carriageway Widths around Curves
Around tight radius curves or corners, additional carriageway width shall be provided to cater for the
swept area of large vehicles and the "cut in" of trailer units in accordance with Table 5.8.
Table 5.8: Minimum Corner and Curve Radii and Carriageway Widths
Inside Corner
Radius or Curve
Radius (m)
Single Lane
Width
(excluding hard
strip provision)
(m)
Two Lane Width for One Way or Two Way Traffic
(excluding hard strip provision) (m)
Inside Lane
Outside Lane
Total
10
8.4
8.4
6.5
14.9
15
7.1
7.1
6.0
13.1
20
6.2
6.2
5.6
11.8
25
5.7
5.7
5.2
10.9
30
5.3
5.3
5.0
10.3
40
4.7
4.7
4.6
9.3
50
4.4
4.4
4.3
8.7
75
4.0
4.0
4.0
8.0
100
3.8
3.8
3.8
7.6
TII Publications
DN-GEO-03060
Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade
separated and compact grade separated junctions)
April 2017
Page 54
5.6.11
Design of Ghost Island Junctions
5.6.11.1
Turning Length
The turning length is provided to allow long vehicles to position themselves correctly for the right turn
off the major road. The turning length shall be 10m long irrespective of the design speed or gradient,
measured from the centreline of the minor road. It is shown on Figure 5.23.
Where capacity calculations indicate that for significant periods of time there
will be vehicles queuing
to turn right from the major road, the turning length shall have a queuing length added to it as a
reservoir to accommodate queuing vehicles.
Figure 5.23: Priority Junction with a Ghost Island
5.6.11.2
Taper Length
Central islands, for ghost islands (Figure 5.24) should normally be developed symmetrically about the
centreline of the major road to the turning lane width at the tapers shown in Table 5.9. The maximum
island width should continue through the junction to the tangent point of the corner radius and the
edge of the major road carriageway, downstream of the direction of the right hand turn as shown in
Figure 5.23. In difficult circumstances, the Designer may relax the taper value by one design speed
step as a relaxation.
Figure 5.24: Ghost Island Development and Taper
