Before revision:  The existence of these regimes and transitions is in agreement with the multiple abrupt phase transitions found for real cities, and represents an important step towards the understanding and optimization of traffic dynamics over coupled road networks .
After revision:  The existence of these regimes and transitions is the spatial separation between the urban center and the periphery, and the number of separate areas that form the periphery. Elaborating on the implications of our results, we show that they may have an influence on the design and optimization of traffic dynamics over coupled road networks .