Highway Engineering

Arm C

QE = 1629 - 0.63Qc

= 1629 - (0.63 ¥248)

=1473 pcu/hr

The ratios of flow to capacity for each entry arm are given in Table 5.5.

130 Highway Engineering

Figure 5.27Graphical representation of entry, exit and circulating flows.

Stream Flow (pcu/hr) Capacity (pcu/hr) RFC

Arm A 619 1433 0.43

Arm B 496 1283 0.39

Arm C 1114 1473 0.76

Table 5.5RFCs for

each entry arm

All movements are below the maximum allowed RFC of 0.85. Arm A is

slightly in excess of 70% so some queuing will occur during peak travel times.

Delays will however not be significant.

5.4.4 Geometric details

The geometric guidelines for roundabout junctions are set out in TD 16/93

(DoT, 1993). While it is not proposed to go into detail on the geometric

considerations that must be addressed when designing a roundabout, the fol-

lowing are brief notes from TD 16/93 regarding design of the following main

parameters: