TII Publications
DN-GEO-03060
Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade
separated and compact grade separated junctions)
April 2017
Page iii
g)
Details specifically for retrofitting existing junctions have
been removed from this
standard and will be incorporated into an updated version of DN-GEO-03030
Guidance on Minor Improvements to National Roads.
DN-GEO-03043 Geometric Design of Priority Junctions and Vehicular Access to National
roads
a)
Conflicts between the Traffic Signs Manual (TSM) and DN-GEO-03043
regarding the provision of diverge tapers and diverge lanes have been reviewed.
b)
Figure 2.2 of DN-GEO-
03043: ‘Approximate Level of Provision of T
-junctions on
New Single Carriageway Roads for various major and minor road Design Year
Traffi
c Flows’ has been removed and guidance on
the approach to traffic
modelling for all junction types has been provided.
c)
Amended corner radii and diverge tapers have been provided in Chapter 5.
d)
Chapter 5 refers to the siting of accesses and junctions on national roads. A
mandatory distance between access roads and Priority Junctions has been
included.
e)
The visibility requirement for drivers emerging from a minor road or direct access
has been updated to be to the high object (1.05m) on the major road as defined
in DN-GEO-03031.
f)
The requirements for channelising islands have been amended to ensure they
are raised and kerbed.
g)
The maximum distance for staggered junctions has been defined.
h)
Table 5.3 from DN-GEO-03043 has been reviewed with regard to the suitability
of left-in/left-out junctions for direct access on single carriageway roads.
i)
The methodology for designing a channelising island has been reviewed and a
step by step process has been provided within an appendix to illustrate the
method.
j)
The siting of a junction on the inside of a curve
has been written into the
document as a Departure from Standards.
k)
The conflict between Paragraphs 7.16 and 7.18 of DN-GEO-03043 with regard
to the maximum allowable gradients on local roads on the approach to a junction
has been clarified.
l)
On the side of the major road opposite a ghost island junction the hard shoulder
shall now be tapered to form a minimum 1.5m hard
strip for new build schemes,
previously 0.5m.
m)
The principles for detailing of roads severed as part of road improvement
schemes have been included in the safety chapter.
DN-GEO-03033 Geometric Design of Roundabouts
a)
A cut-off point between roundabout and link design has been established and
guidance on suitable approach curvature to roundabouts has been provided.
b)
The maximum inscribed circle diameter (ICD) for roundabouts has been revised.
c)
A minimum inscribed circle diameter (ICD) for roundabouts with more than four
arms has been included.
d)
The overrun area diagrams from TAL 12/93 have been reviewed to
clarify that
the stepped pattern is not a requirement.
TII Publications
DN-GEO-03060
Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade
separated and compact grade separated junctions)
April 2017
Page iv
e)
The minimum longitudinal gradients for the circulatory carriageways have been
revised. Similarly, a maximum longitudinal gradient for the circulatory
carriageway has been introduced.
f)
Minimum resultant gradients of the pavement surface on the approach to
roundabouts have been introduced to comply with DN-GEO-03031.
g)
Roundabout types available for use on rural roads are single lane and multi-lane
roundabouts; compact, mini, signalised and double roundabouts have been
removed.
DN-GEO-03035 Layout of Grade Separated Junctions
a)
Layout options were reviewed and Layout Type F Option 1 was
amended to
provide for an additional auxiliary lane.
b)
Direct merge layout A from DN-GEO-03035 has been removed.
c)
Definitions were reviewed to ensure consistency with the definitions of rural
roads in DN-GEO-03036.
d)
Paragraph 4.4 from DN-GEO-03035 has been amended to remove the
reference to TA 58.
e)
Two bridge roundabout layouts and associated text have
been removed from the
standard.
f)
Diamond interchange layouts and associated text have been removed from the
standard.
DN-GEO-03042 Layout of Compact Grade Separated Junctions
a)
Layout options for 4 arm compact grade separation on Single and Dual
Carriageways have been reviewed and updated.
b)
Visibility requirements for low radii connector roads have been updated.