Energy Mix Optimization for Yard Trucks in Container Ports Under Low-Carbon Constraints

With the rapid expansion of global trade, the environmental impacts of port operations have attracted increasing attention. This study develops a mixed-integer programming (MIP) model to identify low-carbon energy mix replacement pathways for yard trucks (YTs), aiming to minimize total cost under low-carbon constraints while accounting for both economic and environmental performance. In the proposed model, the carbon emission cost is separated into transport and idling components to reflect differences in emissions across vehicle operating states. An electric YT (ET) replacement discount coefficient is introduced to quantify the reduction in the effective service capacity of ETs under port operating conditions. The practical significance of the proposed methodology is demonstrated through a case study. The results show that the optimized scheme reduces carbon intensity per unit throughput by 46% over the 15-year planning period, with an average annual decline of 4%. The results also reveal a staged transition pathway: diesel YTs (DTs) are gradually phased out, liquefied natural gas YTs (LNGTs) serve as an interim option, ETs are rapidly deployed and assume a dominant role, and hydrogen fuel cell YTs (HFCTs) increase steadily in the later stages. This study also includes various sensitivity tests, which illustrate that although the magnitude of total cost may vary across different scenarios, the overarching direction of transition remains robust. These findings can inform the formulation of energy mix optimization strategies for YTs.