Figure 4
The system dynamics stock-flow diagram modeling freight transportation, with all original variable names, flows, and connectors: Three main stock (rectangle) variables at the center: “Export underscore Freight underscore Volume underscore In underscore Transit” at the top, “Import underscore Freight underscore Volume underscore In underscore Transit” at the bottom, and “Freight underscore Rate” at the upper right. The flow starts from the left with a cloud, from which an arrow with an inverted triangle labeled “export underscore freight underscore loading underscore rate” leads right to the first main rectangle, which then leads to a cloud at right by an arrow with an inverted triangle labeled “export underscore freight underscore delivery underscore rate.” The system dynamics stock-flow diagram models freight transportation using labeled variables, flows, and connectors. Three main stock (rectangle) variables are arranged at the center and upper right: “Export underscore Freight underscore Volume underscore In underscore Transit” (top center), “Import underscore Freight underscore Volume underscore In underscore Transit” (bottom center), and “Freight underscore Rate” (upper right). The flow starts at the left, where a cloud labeled “historical underscore data underscore export underscore containers” connects via a pipeline with an inverted triangle labeled “export underscore freight underscore loading underscore rate” to “Export underscore Freight underscore Volume underscore In underscore Transit.” From there, another pipeline with an inverted triangle labeled “export underscore freight underscore delivery underscore rate” leads from the rectangle to a cloud on the right. The import process is below: A cloud labeled “historical underscore data underscore import underscore containers” at left leads via “import underscore freight underscore loading underscore rate” to “Import underscore Freight underscore Volume underscore In underscore Transit,” then out via “import underscore freight underscore delivery underscore rate” to a cloud at right labeled “import underscore container underscore delivery.” The rectangle at the upper right, “Freight underscore Rate,” receives flows labeled “change underscore in underscore freight underscore charge” and is influenced by surrounding variables such as “freight underscore charge underscore adjustment underscore time,” “total underscore capacity underscore of underscore truck,” “indicated underscore freight underscore charge,” “Effect underscore of underscore demand underscore and underscore supply underscore balance underscore on underscore freight underscore charge,” “export underscore freight underscore loading underscore rate,” “import underscore freight underscore loading underscore rate,” and “sensitivity underscore of underscore freight underscore charge underscore to underscore demand underscore supply underscore balance.” Circles and diamonds around the stocks represent auxiliary variables and constants: for example, “export underscore freight underscore delivery underscore time,” “truck underscore payload,” “average underscore delivery underscore distance,” “road underscore traffic underscore volume,” “transport underscore speed,” “road underscore transport underscore capacity,” and “the underscore highest underscore speed underscore of underscore trucks underscore on underscore road,” all fully labeled as shown. All arrows and pipelines are shown as directional connectors between variables, following system dynamics conventions.SFD of inland transportation of freight forwarders. Source: Drawn by the authors