Joint scheduling of vertical and horizontal transportation for underground container logistics in seaport terminals.

The underground logistics system is a relatively new concept for container transportation, which is designed to reduce the congestion and pollution on the road caused by the sharply growing number of collections and distributions of containers in the port cities. This paper considers a system where some underground logistics vehicles (ULVs) are marshaled and used to transport containers between two port terminals through a deep underground tunnel. Automated guided vehicles (AGVs) are used for horizontal transportation of containers in the above-ground yard of the terminals, and yard cranes (YCs) are used to transfer the containers vertically through a shaft linking the above-ground yard and the deep underground tunnel. To guarantee the efficiency of this system, a joint scheduling problem of the YCs and the ULVs is proposed and formulated as an integer programming model to minimize the total waiting time of the YCs and ULVs. Taking marshaling and congestion of the ULVs into consideration, a Genetic Algorithm is developed to solve the problem. Numerical experimental results prove the efficiency of the proposed algorithm, and different marshaling strategies are compared. Our research provides a scientific foundation for developing underground logistics systems in large port cities.