LIU Jialin, WU Peiyang, JI Hao, JIA Bin, PENG Zhipeng, SU Bing
China is one of the countries most severely affected by natural disasters, and emergency evacuation is a common and effective measure for disaster prevention and mitigation. In practice, emergency evacuations often require the rapid transfer of some vulnerable populations (e.g., the elderly, pregnant women, and the injured). However, post-disaster road networks may be damaged and congested, severely constraining evacuation efficiency. Electric vertical takeoff and landing (eVTOL) aircraft feature vertical takeoff and landing, obstacle-crossing, and high-speed capabilities, enabling rapid transfer of vulnerable populations and complementing ground transportation to overcome road evacuation bottlenecks. Considering capacity differences and transfer service delays during ground-to-air mode transitions, this paper proposes a ground-air coordinated dynamic evacuation optimization model. In the model, the objective function is to minimize total system evacuation time by jointly deciding the ground-air splitting ratio and path traffic flow. First, the cell transmission model (CTM) is used to characterize the dynamic evolution of ground-air evacuation traffic flows, and a transfer cell mechanism incorporating passenger capacity conversion and transfer service delays is designed. Second, a decomposition algorithm based on the alternating direction method of multipliers (ADMM) is proposed to solve our proposed model. Finally, the effectiveness of the model and algorithm is validated on the Sioux Falls network. The results indicate that: 1) Ground-air collaborative evacuation significantly outperforms only using ground evacuation. The coordinated benefits show a concave growth trend with increasing evacuation demand and tend to stabilize. There exists a globally optimal splitting ratio (approximately 0.38 in the numerical example of this paper) to achieve dynamic resource matching; 2) Ground-air transfer nodes are the core bottleneck restricting the evacuation efficiency of air corridors, where transfer waiting time is significantly longer than flight time and increases at a faster rate; 3) Improving the passenger capacity of eVTOL and the service capacity of take-off and landing points can reduce the total evacuation time, but both exhibit diminishing marginal returns, and the optimal diversion ratio is more sensitive to changes in passenger capacity; 4) The takeoff and landing service capacity and transfer speed of ground-air transfer nodes determine the evacuation efficiency of the air corridor. The improvement of air transport capacity should be matched with transfer service capacity to improve the system's evacuation efficiency. This paper can provide a decision-making support for evacuation plans, route planning, and the allocation of eVTOLs and vehicles during an emergency evacuation.
