# The Environmental Impact of Inland Empty Container Movements Within Two-Depot Systems
## 3 Problem Description  
This section outlines the key components and decisions involved in the inland transportation of empty containers. At its core, these decisions revolve around determining the timing and locations for logistics operations. To make these decisions, a wide range of information is needed, including customer requests, available transportation capacities, and specific factors related to the operational environment. This problem can be considered as one of the most critical and realistic problems, which consists of empty container yards inside ports and multiple inland stations near ports. To understand the problem, we must differentiate between empty container yards and inland freight stations. The role of an empty container yard within port premises is to receive, handle, and temporarily store the empty containers, which typically incur higher storage and handling fees due to the premium value of port space and strict terminal regulations. Additionally, ports often impose short free-storage periods, after which significant demurrage charges apply, incentivizing rapid turnover of empty containers to avoid escalating costs. In comparison, the inland freight station is a designated storage area usually near the port, and offers substantially lower storage fees and extended free-storage periods, making it a cost-effective solution for long-term storage of surplus empty containers. However, this advantage is offset by involving more distance in inland transportation, which directly impacts both transportation costs and CO2 emissions. The greater the distance between the port and the inland freight station, the higher the fuel consumption and associated emissions, making environmental impact a critical factor alongside operational efficiency. Both depots are connected to their hinterlands through inland transportation modes. Along with this, they also provide trans-shipment services and help clear customs, and the related documentation is available at such facilities. Consequently, shipping lines and logistics providers are compelled to minimize dwell times at container yards by swiftly repositioning containers, particularly when immediate demand is absent. Additionally, inland freight stations become favorable for them when inlandporters can be served efficiently, and when avoiding port congestion penalties and demurrage charges is a priority. Undoubtedly, container transportation within two-depot service is required to improve transit reliability, but at the same time, it comes with significant administrative and storage costs. Such costs remain a significant burden in container movements, driven by complex documentation processes, port congestion, and strict storage policies. Furthermore, failure to effectively manage the movement among land depots can increase logistical complexity and reduce efficiency [50; 51]. Since empty containers, in contrast to full containers, need to satisfy an internal demand of the shipping company, there may be more space for CO2 emission and pollution. The rapid increase in the number of vehicles moving empty containers meant that overall emissions continued to rise. Figure 1 illustrates the flow of full and empty containers within the inland transport system. The process starts when full containers arrive at the port through maritime transport and are unloaded for inland distribution. These containers are then delivered to customers using either trucks or trains, depending on the distance and logistics planning. In parallel, empty containers also enter the inland transportation system. They may be repositioned from other regions or returned by customers after unloading. Some are temporarily stored at an empty container yard near the port before being dispatched to inland depots based on demand. The inland transportation between the port, container yard, depots, and customer locations is typically carried out by road or rail.