TII Publications
DN-GEO-03060
Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade
separated and compact grade separated junctions)
April 2017
Page 8
2.2
Priority Junctions
Priority junctions are the most common form of junction control, with the traffic on the minor road giving
way to the traffic on the major road. The advantage of priority junctions is that through traffic on the
major road is not delayed. However, high speeds and/or overtaking traffic manoeuvres on the major
road should be discouraged at priority junctions. For more heavily used junctions, more complex forms
of junction layout are required.
Priority junctions can be categorised by the configuration of the minor road(s) in
relation to the major
road as described below. Priority junction types are described in further detail in Chapter 5.
2.2.1
T-Junction
An at-grade junction of two roads, at which the minor road joins the major road approximately at right
angles as shown in Figure 2.1.
Figure 2.1: Simple T-Junction
2.2.2
Staggered Junction
An at-grade junction of three roads, at which the major road is continuous through the junction, and
the minor roads connect with the major road so as to form two opposing T-junctions at a minimum
distance apart (Figure 2.2).
TII Publications
DN-GEO-03060
Geometric Design of Junctions (priority junctions, direct accesses, roundabouts, grade
separated and compact grade separated junctions)
April 2017
Page 10
2.2.4
Traffic Control at Priority Junctions
Priority junctions can be further distinguished by the type of traffic control used at the junction. These
traffic controls include:
a)
Simple Junction
–
A “T
-
” or staggered junction without a ghost island in the
major
road. Channelising islands can be provided in the minor road approach (Figure
2.1).
b)
Ghost Island Junction
–
An at-grade junction, usually a T- or staggered junction,
within which an area is marked on the carriageway, shaped
and located so as to
direct traffic movement by providing means of a right turning lane. A channelising
island shall be provided in the minor road approach (Figure 2.4).
Figure 2.4: Ghost Island Junction
c)
Left-In/Left-Out Junction
–
An at-grade junction where left turn movements only
are permitted onto and off the minor road. Sign posting
and physical lane
segregation are used to prevent any right turning movements. Figure 2.5 shows an
indicative layout for a left in/left out junction at a direct access.
d)
Signalised Priority Junctions
–
Priority junctions incorporating traffic signals
shall generally not be provided on national roads and require a Departure from
Standards where they are proposed for incorporation into a national road scheme.