Question

In a four phase signal, the critical flow rate in the last 3 phases is 250,200,275 veh/hr respectively. If the saturation flow rate for all the phases is 2000veh/hr, and lost time is 3 sec per phase with cycle length as 65 sec, the critical flow rate for first phase is

• A. 567 veh/hr
• B. 587 veh/hr
• C. 577veh/hr
• D. 557 veh/hr

Answer 1

The correct option is A 567 veh/hr

Cycle length $C=\frac{1.5L+5}{1-y}$
Total lost time = 3 x 4 = 12 sec
$65=\frac{1.5\times 12+5}{1-y}$
Y = 0.646

Flow ratio for second phase $=y_2=\frac{250}{2000}=0.125$
For third phase = $y_3=\frac{200}{2000}=0.1$

For fourth phase = $y_4=\frac{275}{2000}=0.1375$

$y=y_1+y_2+y_3+y_4$

0.646=$y_1$+ 0.125 + 0.1 + 0.1375
$y_1=0.2835$

flow rate in first in phase = 0.2835 x 2000 = 567 veh/hr