Highway Engineering

The Design of Highway Intersections 109

Example 5.1 Contd

be upgraded to a ghost island junction. Using these AADT values, the 2-way
annual average hourly traffic (AAHT) on all three arms can be computed by
dividing each AADT value by 24, giving the results shown in Fig. 5.7.

313 to 427 vehicles/hr

83 to 125 vehicles/hr

313 to 427 vehicles/hr

Figure 5.7AAHT flows.

It is decided on economic grounds to design the junction to cater for the
thirtieth highest annual hourly flow. On the basis of local traffic count data,
it is found that the AAHT flow on each of the approach roads is translated
into a design peak hour flow by multiplying by a factor of 3.0, with the results
shown in Fig. 5.8.

939 to 1281 vehicles/hr

249 to 375 vehicles/hr

939 to 1281 vehicles/hr

Figure 5.8Design peak hour flows (2-way).

Directional splits derived from local traffic data are applied to these design
flows in order to obtain the final directional flows, in this case a 70:30 split
in favour of flows from the southern and eastern approaches, as shown in
Fig. 5.9.

282 to 384

vehicles/hr

174 to 263

vehicles/hr

657 to 897

vehicles/hr

Figure 5.9Directional flows from all arms.

Contd