Highway Engineering

give priority to the major road with traffic from it only entering the major road

when appropriate gaps appear. The principal advantage of this type of junction

is that the traffic on the major route is not delayed.

The principle at the basis of the design of priority intersections is that it

should reflect the pattern of movement of the traffic. The heaviest traffic flows

should be afforded the easiest paths. Visibility, particularly for traffic exiting the

minor junction, is a crucial factor in the layout of a priority intersection. Low

visibility can increase the rate of occurrence of serious accidents as well as

reducing the basic capacity of the intersection itself.

Priority intersections can be in the form of simple T-junctions, staggered junc-

tions or crossroads, though the last form should be avoided where possible as

drivers exiting the minor road can misunderstand the traffic priorities. This may

lead to increased accidents.

Diagrammatic representations of the three forms are given in Fig. 5.1.

106 Highway Engineering

Simple T-junction Staggered T-junction Crossroads junction (not

recommended)

C A

B

C A

B

D

C A

B

D

Figure 5.1Three forms of priority intersection.

Within the two main junction configurations mentioned above (T-

junction/staggered junction), there are three distinct types of geometric layout

for a single-carriageway priority intersection:

 Simple junctions:A T-junction or staggered junction without any ghost or

physical islands in the major road and without channelling islands in the

minor road approach (see Fig. 5.2).

Figure 5.2Simple

T-junction.