There are two key points in order to obtain the coordinated control of the green wave of traffic lights: the same period and the same clock.

The so-called common period refers to the intersection with the smallest traffic capacity or the intersection with the largest overall traffic load among the intersections with coordinated demand signals. The signal period after signal timing calculation is used as the common period of all intersections. Because according to the "barrel principle" of management, the intersection with the smallest traffic capacity is the bottleneck of the road or road network. If this intersection can pass traffic, other intersections must also be able to pass. Therefore, under normal circumstances, the intersection with the smallest traffic capacity has the longest signal cycle. If this cycle is used as the cycle of all intersections, no congestion will occur at other intersections.