Transport geography can be better understood from a series of eight core principles:
- Transportation is the spatial linking of a derived demand. It occurs because of other economic activities that link its spatial components through flows of people, goods, and information. For instance, commuting is the spatial linking of labor flows resulting from the demand for labor at one location (e.g., a commercial district) and its supply at another (e.g., a residential district). Distribution links providers of parts and finished goods to the demand, such as final consumers or manufacturers. A market economy could not function without the capacity of transportation to link supply and demand, allowing for transactions to literally “take place”.
- Distance is a relative concept involving space (how much is accessible), time (the duration of transportation), and effort (the cost or energy expense). How distance is perceived is a function of the effort required to overcome it, commonly expressed as transport costs that indirectly reflect the friction of distance. A longer physical distance traveled with ease (e.g., at low cost or in a short amount of time) implies less friction than a shorter physical distance subject to delays, congestion, and high costs.
- Space is simultaneously the generator, support, and constraint for mobility. Space is the support for mobility as it will shape the nature and structure of the transport system. Spatial differences in attributes such as resources, employment, and population act as generators and attractors of movements. How space constrains transport is often relative and paradoxical. For instance, oceans and rivers act as constraints for land transport systems such as roads and railways, but can support maritime transportation. While the atmosphere provides the physical support for air transport operations (air corridors), weather can be a constraining factor under specific conditions (e.g., snowstorms, thunderstorms, hurricanes). Further, transportation is a space by itself, an activity space, implying that socioeconomic activities are taking place during the transportation process, either in modes or at terminals.
- The relation between space and time can converge or diverge. Every form of transport involves the consumption of a unit of time in exchange for a given amount of space (this is how speed is measured). Over time, this process has mostly converged, implying that more space can be reached in the same amount of time (or the same amount of space can be reached in less time). This is the result of technological improvements as well as greater capacity and extent of transport infrastructure. The relationship between space and time can also diverge when congestion becomes significant, and each additional unit of movement increases delays. Disruptions in a transport system, such as accidents, equipment failures, or weather events, commonly create a temporary space-time divergence as capacity is lost.
- A location can be a central or an intermediate element of mobility. Locations are central when they act as generators (origins) or attractors (destinations) of movements. Locations are labeled as intermediate when movements are passing (transiting) through on their way to other locations. The structure of transportation networks coordinates the centrality and intermediacy of locations. Hubs usually involve intermediacy within the same mode, while gateways concern intermediacy between modes. Ports and airports are often intermediate locations, serving as gateways or hubs within complex transport networks.
- To overcome geography, transportation requires a footprint. Transportation infrastructure is an important consumer of space, including rights-of-way (e.g., roads and rail lines) and terminals. Jointly, they form transportation networks. The more extensive a transport system and the higher its mobility level, the larger its footprint. For instance, roads and parking spaces can consume up to 50% of the land in highly motorized cities. Globalization has been linked with the setting of massive terminal facilities such as container ports, airports, and distribution centers. While space consumed by road infrastructure is mostly linked to local and regional activities, the space consumed by rail, port, and airport terminals is linked to activities on a larger scale.
- Transportation seeks massification but is constrained by atomization. Transport systems are most effective when they achieve economies of scale, particularly in the loads (passengers or freight) they can carry. Massification involves conveyances with higher capacity and supported by larger terminals. However, the first and last segments of a transport sequence may require atomization, which implies that transport loads (passengers or freight) must be consolidated and deconsolidated. For instance, passengers taking a flight must be consolidated into a planeload at an airport terminal and deconsolidated at the destination airport. So, the higher the level of massification, the more complex atomization becomes. Massification conveys benefits but restricts mobility options, while atomization is more expensive but provides more mobility options. Although public transit can technically be more cost-efficient, many prefer individual (atomized) modes of transportation, such as the automobile, because of their point-to-point capabilities.
- Velocity is a modal, intermodal, and managerial effort. Velocity does not necessarily mean speed; it refers to the time it takes for a passenger or a unit of freight to move along a transport chain. For instance, the speed advantage of air transportation is undermined if a passenger spends several hours between connecting flights. Therefore, the velocity of passengers or freight is a joint consideration of the effectiveness of the respective modes involved and of the intermodal operations connecting them. Also, the complexity of transport systems requires effective operational management, such as scheduling, booking, and settlement of transactions (e.g., fares). Logistics has become a key activity for ensuring that freight is distributed effectively across geographies. All of the above jointly contribute to improving the velocity of flows carried by transport systems. Recent efforts at the digitalization of transportation aim to increase the velocity of transportation through better management of existing assets and by creating exchange platforms between providers and users of transportation services.