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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 |
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