Computer networks and telecommunication systems are often described by a conceptual model called layers. Every layer uses the services of the lower layers to fulfil its own services. This abstraction allows to discuss each layer separately, evolving and changing them without breaking the functionality of the upper layers. It also allows to create heterogenous networks, where each node might be connected using different physical connections. The same conceptual model can be used to describe the transportation system. It also forms a heterogenous network of many nodes all over the world. Instead of information, it transports humans and physical goods. This article introduces the use of the layering analogy to the transportation system, analyzes its structure and identifies the different roles that comprise this network.
