Highway Engineering

Values of entry and circulating flows

In order to estimate the circulating flow and thus the entry capacity of each

entry movement using the manual procedure, the entry flow values from

Fig. 5.25 are multiplied by a factor of 1.125. The derived flows are then

multiplied by 1.1 in order to convert the vehicles to passenger car units (pcu)

(Table 5.4).

128 Highway Engineering

Example 5.4 Contd

Estimate the ratio of flow to capacity for each entry point. A heavy goods

vehicle content of 10% is assumed.

The following are the geometric parameters assumed for each entry arm

at the junction:

e =7.5 m

v =4m (east and west arms), 3.65 m (south arm)

l¢=10 m

D =28 m

f =30°

r =10 m

Therefore

k =0.951

S =0.56 (east and west arms), 0.62 (south arm)

X 2 =5.65 (east and west arms), 5.37 (south arm)

F =1712 (east and west arms), 1629 (south arm)

M=0.0408

tD=1.48

fc =0.662 (east and west arms), 0.645 (south arm)

For east arm (Arm A):

QE=k(F-fcQc)

=0.9511(1712 -0.6622Qc)

= 1629 - 0.63Qc

For south arm (Arm B):

QE=k(F-fcQc)

=0.951(1629 -0.65Qc)

= 1549 - 0.614Qc

For west arm (Arm C):

QE=k(F-fcQc)

=0.9511(1712 -0.662Qc)

= 1629 - 0.63Qc