Green Split Calculations

Assuming that both of the critical movements in a two-phase cycle have the same saturation flow rate, what percentage of the available green time would each phase receive, given the design flow rates for the critical movements listed below?

 Situation Number Phase 1 Flow Rate (pcu/hr) Phase 2 Flow Rate (pcu/hr) 1 500 250 2 400 100 3 90 30 4 100 80

[Solution Shown Below]

Solution

The available green time is allocated based on the ratio of the critical flow ratios to the sum of the critical flow ratios. However, in this case we can simplify the calculations because the saturation flow rate is assumed to be identical for both of the critical movements. This means that the green time is allocated according to the ratios of the design flow rates to the sum of the design flow rates. This simplification is shown below.

gi = G*((V/s)i/(S(V/s)) --- simplifies to--->   gi = G* Vi/SV

Since we weren't given the available green time, we'll forget about it and focus on the ratios. For situation number one, the design flow rate for the critical movement in phase one was 500 pce/hr while the critical design flow rate for phase two was 250 pcu/hr. The sum of these flow rates is 750 pcu/hr. Hence, phase one will receive 67% (500/750) of the available green time, while phase two will receive 33% (250/750). The results are tabulated below.

 Situation Number Phase 1 Flow Rate (pcu/hr) Phase 2 Flow Rate (pcu/hr) Phase 1 % of G Phase 2 % of G 1 500 250 67 33 2 400 100 80 20 3 90 30 75 25 4 100 80 56 44