oa Evaluating the potential of using truck appointment systems to decrease reefer energy consumption at container terminals

In the recent decades there has been an unprecedented globalization of trade. One of the most important factors that made this possible is the containerization of the supply chain. As a consequence container terminals have become essential for todays globalized economy. The trend of containerization has further extended to the cold supply chain through the use of reefers (refrigerated containers), resulting in a tremendous increase in the trade of food and other perishable goods. In case of import dependent countries like Qatar the cold supply chain has become essential for food security. The number of reefers at container terminals has substantially grown and as a consequence their energy use. In average ports, the largest part of energy is consumed by crane operations and cooling of reefers. In case of ports that are dedicated to export/import of foods the cooling of reefers becomes the largest component of terminal energy consumption. This is especially the case in countries with extreme temperatures like Qatar. Although there has been a substantial amount of research dedicated to optimizing operational procedures of cranes at container terminals with a focus on minimizing energy use, similar approaches have not been explored in case of reefers and the related cold supply chain. In this work we focused on the potential of exploiting a terminal truck appointment system (TAS) to this goal. The main objective of the TAS is to minimize the waiting times at the port gates and to maximize the utilization of container yard equipment. It is important to note that previous research has shown that the information from the TAS can be used to optimize the crane operations. The majority of the existing research on TAS systems has been dedicated to evaluating the potential benefits that such systems can bring to a port in the sense of truck turn times. The concept of including reefer related information into a TAS adds a new dimension to the problem. This is due to the fact that the energy use of a reefer container is directly related to its dwelling time. The idea is to minimize the stay of reefers at the port. To be more precise the objective is to minimize the time since a reefer is unloaded to the port until a truck takes it out of the port. In practice this means that we wish to get the trucks that import the reefers to come to the port as soon as possible. This type of work adds a new type of objective where there is a higher priority related to trucks importing reefers. It is possible to develop a mixed integer program to assist in designing optimal methods for TAS related issues it is often not the best choice. The problem is that due to the high level of unpredictability in the movement of trucks inside and outside of the port the evaluation of a TAS system in this way is often not adequate. Due to this fact, the evaluation of such systems is frequently done using discrete event simulations (DES). In the existing literature the schedule for trucks is fixed, and further analysis is done to evaluate the effect of missed appointments and the percentage of «walk-in» trucks. The DES is only used for the truck arrivals to the port and related use of resources (Entrance Gate, Yard, Exit Gate, etc.). In the proposed research we extend the DES to also include dynamic appointment scheduling. To be more precise, we analyze how requests arrive and how appointments are given. This is important in the context of reefers since we want to give then higher priority, in the sense of leaving appointment slots open for truckers that transport them out of the port, which would otherwise be booked. The proposed DES is used to evaluate several strategies for appointments systems for both minimizing turn times of trucks and the dwelling times of containers. We show that some strategies can notably decrease the energy used for reefer cooling while maintaining short truck turn times.