Determine Critical Lane Groups and Total Cycle Lost Time For any combination of lane group movements during a particular timing stage, one of these lane groups will control the necessary green time for that timing stage. This lane group is referred to as the critical lane group. When the traffic movements of each lane group occur during only one timing stage of the signal cycle, the determination of the critical lane group for each timing stage is straightforward. In this case, the critical lane group for each phase is simply the lane group with the highest ratio of vehicle arrival rate to vehicle departure rate (λ/μ). This quantity is referred to as the flow ratio (which was called the traffic intensity, ρ) and is designated v/s (arrival flow rate divided by saturation flow rate). If the allocation of green time for each timing stage is
based on the flow ratio of the critical lane group, then the noncritical lane group movements will be accommodated as well.
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With dual-ring controllers, a wide variety of phasing sequences is possible. The situation where a phase starts in one signal timing stage and continues in the next signal timing stage is referred to as an overlapping phase. For the case of overlapping phases in a signal cycle, the identification of the critical lane groups is more complex, as the lane group with the highest flow ratio in each timing stage is not necessarily the critical lane group for that timing stage.