The physics of green-wave breakdown in a city

The physics of the breakdown of a green wave (GW) in a city is revealed. We have found that there are two regions of flow rates in the GW within which the GW breakdown is possible. In the region of larger flow rates bounded by the maximum capacity and threshold flow rate, a time-delayed spontaneous GW breakdown occurs with some probability during a given observation time. In the region of smaller flow rates bounded by the threshold flow rate and minimum capacity, only an induced GW breakdown is possible. The GW breakdown can be simulated with traffic flow models in the context of either three-phase or two-phase theories. However, in three-phase models the spontaneous GW breakdown is initiated by the emergence of a moving synchronized flow pattern (MSP); the MSP results from an initial speed disturbance at the beginning of the GW. In contrast, in two-phase models no MSPs can occur, therefore, considerably heavier conditions for both spontaneous and induced GW breakdowns are found.