Empirical Investigations on Traffic Phase Transitions at Beijing Ring Road

In this paper, traffic features of urban ring road are investigated based on empirical data of Beijing 2^nd Ring Road. According to the concept of "synchronized flow" as well as the stability and synchronization among lanes around critical density, four traffic phases are identified: free flow, high-speed synchronized flow, low-speed synchronized flow and traffic jam. Moreover, spatio-temporal features of traffic flow based on these four phases are investigated empirically.