Highway Engineering

The fully factored flows entering, exiting and circulating within the round-
about are illustrated diagrammatically in Fig. 5.26 and graphically in Fig. 5.27.

The Design of Highway Intersections 129

ARM A ARM B ARM C

qAB qAC qBA qBC qCA qCB

Flow in veh/hr 150 350 200 200 650 250

Flow in pcu/hr (¥1.1) 165 385 220 220 715 275

Factored flow (¥1.125) 186 433 248 248 804 310

Factored entry flow (pcu/hr) 619 495 1114

Factored circulating flow (pcu/hr) 310 433 248

Table 5.4Entry flows

Figure 5.26Factored entry, circulating and exiting flows (pcu/hr).

Entry capacities

Given the circulating flows estimated above, the entry capacity for each of the
three arms can be computed as:

Arm A
QE= 1629 - 0.63Qc
= 1629 - (0.63 ¥310)
=1433 pcu/hr

Arm B
QE= 1549 - 0.614Qc
= 1549 - (0.614 ¥433)
=1283 pcu/hr