Spatiotemporally coordinated scheduling of suspended monorail vehicles and AGVs under a double cycling strategy in automated container terminals

The intelligent bidirectional suspended monorail system connects the yard with the near-dock rail terminal, providing an effective “last mile” solution for sea-rail intermodal transport in automated container terminal. The suspended monorail vehicle (SMV), operating along fixed tracks, is capable of both horizontal container transport and vertical handling. Efficient coordination between SMVs and automated guided vehicles (AGVs) is essential for enhancing overall terminal performance. This study investigates the spatiotemporally coordination scheduling of SMVs and AGVs under a double-cycling strategy. A mixed-integer linear programming model is formulated to minimise the overall makespan while satisfying track safety constraints for SMV operations. To efficiently solve the proposed model, an enhanced logic-based Benders decomposition (E-LBBD) algorithm is developed, in which the master problem determines task assignment decisions and the subproblem resolves the coordinated scheduling of SMVs and AGVs, with several acceleration strategies are incorporated to improve computational performance. Computational experiments demonstrate that: (i) The proposed E-LBBD algorithm, enhanced by tailored acceleration strategies, significantly outperforms Gurobi in terms of computational efficiency. (ii) Synchronising AGVs with SMVs under a double-cycling strategy not only reduces the makespan but also lowers empty travel, outperforming both single-cycling and flexible scheduling strategies. (iii) Balancing the fleet sizes of SMVs and AGVs, along with appropriately setting stage-specific operation time parameters, can further enhance overall terminal performance.