Abstract: With the continuous development of container transportation business, the efficiency and management level of container terminal is more and more important. At the same time, the problem of yard trailers routing receives more attention because yard trailers work as the main machine to carry containers in the horizontal direction at terminals. However, most current research on yard trailers routing problem did not consider the influence of no-load distance on trailers' transport efficiency, and a large part of current research just made routing optimization for singer yard trailers ignoring the condition of different trailers. Under the above background, a two-stage routing optimization model which consisting of two relevant models for yard trailers is proposed to solve the routing problem based on pool strategy. This strategy means loading and unloading operations are performed during one work route instead of doing loading and unloading operations separately. On the first stage, a routing optimization model is given to minimize the route distance without considering the number of yard trailers. This model is used to determine which import and export blocks to go through. On the second stage, for the purpose of minimizing no-load distance, the other routing optimization model which considers the number of trailers is constructed based on the result of the first model. According to the characteristics of two models, the software of Lingo is used to solve the first model, and particle swarm optimization method is utilized to solve the second model which involves route assignment and job order for every trailer. The results show that the no-load distance and no-load rate are decreased after the optimization on the second stage. In addition, with the second stage model, it is found that increasing the number of trailers is helpful to reduce the no-load rate. By proposing the two-stage routing optimization model, both the no-load distance and the number of yard trailers are taken into account and improves the existing research.

Key words: container terminals, yard trailers, two-stage routing optimization, particle swarm optimization