Eco-Efficient Scheduling at the Three Gorges Ship Lock: A Dual-Objective Epsilon-Constraint Approach to Balancing Transit Time and Emissions

The Three Gorges Ship Lock is an important hub in China’s inland waterway shipping system. Our study unifies the low-carbon goals with lock scheduling and minimizes the total navigation and lock passage time as well as CO₂ emissions simultaneously through a dual-objective mixed integer programming. The model handles the discrete selection of the pre-lock speed, the allocation of ship-batch-lock chambers, and the two-dimensional arrangement within the lock chambers, and ensures the feasibility of the solution with safety spacing and emission budget. It innovatively adoptes the ε -constraint method for solution. The experiment covers instances of different scales. On the instances of 20 ships and 50 ships, the total waiting time of the ε -constraint is lower. On the 80-ship instance, the ε -constraint demonstrates significant advantages: the average emissions decreased by 52.9%, the total time dropped by 35.3%, and the average gap decreased from 71.34% to 56.40%. The results show that the ε -constraint method approaches the time-emission compromise solution more stably, especially in large-scale instances, it can effectively reduce emissions and travel time. The established model and the adopted epsilon constraint method can provide empirical basis and methodological foundation for the green scheduling of inland river hub locks.