Mixed Traffic Flow Evacuation In City Emergency

Large scale evacuation dynamics in urban area has been recognized as an interdisciplinary complex problem. Currently, most studies focuse on the evacuation process inside the buildings or outside the building, taking the single form of walking or by vehicle. However, evacuation under circumstances of mixed traffic flow is more common in China due to the diversities of modern transportation ways. Consequently, it is an important problem to understand how the mixed traffic flow affects the evacuation time and the potential means of effectively increasing the evacuation efficiency, such as improving the utilization of the road. Thus, the investigation of the urban evacuation with mixed traffic flow in emergency will suggest some scientific significance to the evacuation planning for emergency management in our country, especially to the evacuation strategies for walking.To comprehensively describe the complex evacuation process with mixed traffic flow, we have considered various factors and provided a framework for the analysis of realistic urban evacuation models. The current model consists of three modules: transportation network module, discrete dynamical macro-analysis module, and individual-based evacuation simulation module.The transportation network module describes the transportation infrastructure, objects to evacuate, and the emergency information based on the GIS transportation network data, which provids a simulating environment for the other two modules. The discrete dynamical macro-analysis module is responsible for updating some parameters, which contains several sub-models such as traffic generation, evacuation site selection, evacuation path selection, post-disaster traffic capacity evaluation, and transportation tools selection. The individual-based evacuation module is the key part in this paper, implementing two switching ways between traffic generation model and the normal traffic evacuation. And the rules of switching roads and intersection conflicting avoidance for vehicles, bicycles, and pedestrians have been well designed respectively. Finally, based on the cellular automata, performed extensive simulations are conducted and analyzed, with main results listed below.In this paper, the change of traffic flow for different road sections and transportation tools is studied through simulations, road condition and the reasons that lead to traffic jam can be obtained. How the decision of transportation tools affects the evacuation time is discussed to get the optimized evacuation time. We also study the effect of different traffic control strategies, like speed limits and the isolations between vehicle lane and non-motor lane. Conclusions will provide support for evacuation planning and emergency evacuation traffic control decision.