Freight Models: The Basics
In freight transport, multiple stakeholders, referred to as “agents,” are involved in a chain of business transactions. These agents include manufacturers, shippers, carriers, purchasers, and consumers, among others. Each agent makes decisions that are rational, similar to how we assume individual commuters optimize their travel mode, destination, and route choices.
Freight modeling shares some similarities with passenger transportation modeling. Both involve a representation of demand (the desired movement of goods or people) and one of supply (the transportation network and its characteristics). Similar processes, such as static traffic assignment, are often used. However, modeling freight differs significantly from modeling personal travel due to the complexity of the involved processes. Unlike a commuter’s travel decision, which is a standalone economic action, the decisions made by freight agents form a linked sequence known as the “supply chain,” encompassing the entire journey from raw materials to the final product delivered to the consumer. Moreover, freight modeling must account for logistical considerations such as warehousing. These factors add layers of complexity that do not typically exist in personal travel modeling. Additionally, freight movement is influenced by broader economic trends, regulatory environments, and technological advancements.
Main Types of Freight Models
Various types of freight models offer distinct approaches and insights, each suited to different aspects of freight movement and logistics. Below is an overview of the four most commonly found types of freight models:
- Four-Step Models: These are traditional models that predict freight movement through a sequence of four steps: trip generation, trip distribution, mode choice, and route assignment. They can be:
- Vehicle-Based Models: Focused on the movement of freight vehicles.
- Commodity-Based Models: Focused on the movement of goods.
- Tour-Based Models: These models focus on the sequence of stops a freight vehicle makes, offering a more comprehensive view of freight activity and vehicle utilization.
- Agent-Based Models: These simulate the behavior of individual entities (e.g., trucks, shippers) to capture the complexity and variability of freight movement.
- Logistics/Supply Chain Models: These models analyze the entire supply chain, from production to delivery, allowing the use of intermediate stops to represent distribution channels.
More detailed information on freight model characteristics and applications can be found here.