Source: adapted from Taaffe, E.J., H.L. Gauthier and M.E. O’Kelly (1996) Geography of Transportation, Second Edition, Upper Saddle River, NJ: Prentice Hall.
The development of transportation networks commonly leads to the creation of corridors through the spatial concentration of flows along a core axis. A corridor development model has been developed by Taaffe, Morrill, and Gould (1963) to explain this process in the Western African context (particularly Ghana and Nigeria). It can be applied elsewhere, such as in North America, but the timing of each phase may vary substantially depending on the region:
- Phase A (Scattered ports). A set of small trade ports is established along a coastline. They are connected to a wider network of trade and provide access to locally supplied resources. This process can take place over centuries as it was the case for the global port system prior to the industrial revolution.
- Phase B (Penetration lines and port concentration). Trade corridors accessing the hinterland are constructed permitting the development of new resources and/or markets. The ports to which they are connected grow in proportion to the new traffic generated. This is representative of the early stages of the industrial revolution where the first canal and rail connections were established.
- Phase C (Development of feeders). The hinterland of penetrating lines is further expanded by the development of feeders. This represents the early stages of rail corridor developments.
- Phase D (Beginning of interconnections). The transport networks that have so far been developing independently gradually become interconnected. Intermediate centers also start to emerge along with the first road systems. The setting of rail corridors is peaking.
- Phase E (Complete interconnection). As the level of connectivity increases, traffic tends to concentrate in the most connected ports (often corresponding to the largest cities), implying that several less well-connected ports decline or disappear. This phase usually implies the rapid construction of highway systems supporting existing rail corridors as well as the setting of air connections between large city-pairs.
- Phase F (Emergence of high priority links). Economies of scale favor the concentration of the traffic along with the most efficient ports and links, supporting the emergence of transport corridors. Links having lower volumes can even be shut down. The regional transport system has thus reached a phase of maturity and the structure of the network is unlikely to change unless of significant economic or technological developments.