1. The Spatial Organization of Transportation

Throughout history, transport networks have structured space at different scales. The fragmentation of production and consumption, the locational specificities of resources, labor and markets generate a wide array of flows of people, goods and information. Transportation not only favors economic development but also has an impact on the spatial organization. Space shapes transport as much as transport shapes space, which is a salient example of the reciprocity of transport and its geography. This reciprocity can be articulated over two points:

• This relationship concerns the transport system itself. Since the transport system is composed of nodes and links as well as the flows they are supporting the spatial organization of this system is a core defining component of the spatial structure. Even if streets are not the city, they are the means that are shaping its organization in terms of locations and relations. The same apply for maritime shipping networks, which are not international trade, but reflect the spatial organization of the global economy.
• This relationship concerns activities that are all dependent on transportation at one level or another. Since every single activity is based on a level of mobility, they relationship they have with transportation is reflected in their spatial organization. While a small retail activity is conditioned by local accessibility from which it draws its customers, a large manufacturing plant relies on accessibility to global freight distribution for its inputs as well as its outputs.

The more interdependent an economy is, the more important transportation becomes as a support and a factor shaping this interdependence. The relationship between transport and spatial organization can be considered from three major geographical scales; the global, the regional and the local.

2. Global Spatial Organization

At the global level, transportation supports and shapes economic specialization and productivity, through international trade. Improvements in transport are expanding markets and development opportunities, but not uniformly. The inequalities of the global economy are reflected in its spatial organization and the structure of international transport systems. The patterns of globalization have created a growth in spatial flows (trade) and increased interdependencies. Telecommunications, maritime transport and air transport, because of their scale of service, support the majority of global flows. The nature and spatial structure of these flows can be considered from two major perspectives that seek to explain global differences in growth and accessibility:

• Core / periphery. This basic representation assumes that the global spatial organization favors a few core areas that grow faster than the periphery. Differential growth creates acute inequalities in levels of development. Transportation is thus perceived as a factor of polarization and unequal development. From this perspective, parts of the global economy are gaining, because they are more accessible, while other are marginalized and bound to dependency. However, this trend can be reversed if international transport costs are significantly reduced. This is evidenced by the substantial growth of many Pacific Asian countries that have opted for an export oriented strategy which requires good access to global freight distribution. Consequently, the core / periphery relationship is flexible.

• Poles. Transportation is perceived as a factor of articulation in the global economy where the circulation of passengers and freight is regulated by poles corresponding to a high level of accumulation of transport infrastructures, distribution and economic activities. These poles are subject to centrifugal and centripetal forces that have favored geographical concentration of some activities and the dispersion of others. The global economy is thus based on the backbone of freight distribution, which in turn relies on networks established to support its flows and on nodes that are regulating the flows within networks. Networks, particularly those concerning maritime shipping and air transportation, are flexible entities that change with the ebb and flows of commerce while nodes are locations fixed within their own regional geography.

The global spatial organization is a priori conditioned by its nodality. Global flows are handled by gateways and hubs, each of which account for a significant share of the flows of people, freight and information.

Gateway. A location offering accessibility to a large system of circulation of freight and passengers. Gateways reap the advantage of a favorable physical location such as highway junctions, the confluence of rivers, a good port site, and have been the object of a significant accumulation of transport infrastructures such as terminals and their links. A gateway is commonly an origin, a destination and a point of transit. It generally commands the entrance to and the exit from its catchment area. In other words, it is a pivotal point for the entrance and the exit in a region, a country, or a continent and often requires intermodal transfers.

Hub. A central point for the collection, sorting, transshipment and distribution of goods for a particular area. This concept comes from a term used in air transport for passengers as well as for freight and describes collection and distribution through a single point such as the “Hub and Spoke” concept.

Services are following a spatial trend which appears to be increasingly different than of production. As production disperses worldwide to lower cost locations, high level services increasingly concentrate into a relatively few large metropolitan areas, labeled as world cities. They are centers for financial services (banking, insurance), head offices of major multinational corporations and the seats of major governments. Thus, gateways and world cities may not necessarily correspond as locations. This is particularly the case for containerized traffic which is linked with new manufacturing clusters and the usage of intermediary locations such as offshore hubs.

3. Regional Spatial Organization

Regions are commonly organized along an interdependent set of cities forming what is often referred as an urban system. The key spatial foundation of an urban system is based on a series of market areas, which are a function of the level of activity of each center pondered by the friction of distance. The spatial structure of most regions can be subdivided in three basic components:

• A set of locations of specialized industries such as manufacturing and mining, which tend to group into agglomerations according to location factors such a raw materials, labor, markets, etc. They are often export oriented industries from which a region derives the bulk of its basic growth.
• A set of service industry locations, including administration, finance, retail, wholesale and other similar services, which tend to agglomerate in a system of central places (cities) providing optimal accessibility to labor or potential customers.
• A pattern of transport nodes and links, such as road, railways, ports and airports, which services major centers of economic activity.

Jointly, these components define the spatial order of a region, mostly its organization in a hierarchy of relationships involving flows of people, freight and information. More or less well defined urban systems spatially translate such development. Many conceptual models have been proposed to explain the relationships between transport, urban systems and regional development, the core-periphery stages of development and the network expansion being among those. Three conceptual categories of regional spatial organization can be observed:

• Central places / urban systems models try to find the relationships between the size, the number and the geographic distribution of cities in a region. Many variations of the regional spatial structure have been investigated by the Central Place Theory. The great majority of urban systems have a well established hierarchy where a few centers dominate. Transportation is particularly important in such a representation as the organization of central places is based on minimizing the friction of distance. The territorial structure depicted by Central Place Theory is the outcome of a region seeking the provision of services in a (transport) cost effective way [Preston, 1985].
• Growth poles where economic development is the structural change caused by the growth of new propulsive industries that are the poles of growth. The location of these activities is the catalyst of the regional spatial organization. Growth poles first initiate, then diffuse, development. It attempts to be a general theory of the initiation and diffusion of development models. Growth gets distributed spatially within a regional urban system, but this process is uneven with the core benefiting first and the periphery eventually becomes integrated in a system of flows. In the growth poles theory transportation is a factor of accessibility which reinforces the importance of poles [Perroux, 1955].
• Transport corridors represent an accumulation of flows and infrastructures of various modes and their development is linked with economic, infrastructural and technological processes. When these processes are involving urban development, urbanization corridors are a system of cities oriented along an axis, commonly fluvial or a coastline. Corridors are also structured along articulation points that regulate the flows at the local, regional and global levels. Historically, urbanization was mainly organized by the communication capacities offered by fluvial and coastal maritime transportation. Many urban regions such as BosWash (Boston - Washington) or Tokaido (Tokyo - Osaka) share this spatial commonality.

4. Local Spatial Organization

Although transport is an important element in rural spatial organization, it is at the urban level that transportation has the most significant local spatial impact. Urbanization and transport are interrelated concepts (see Chapter 6 for a detailed perspective concerning urban transportation). Every city relies on a need for mobility of passengers (residence, work, purchases, and leisure) and freight (consumption goods, food, energy, construction materials and waste disposal) and where the main nodes are employment zones. Urban demographic and spatial evolution is translated in space by the breadth and amplitude of movements. Employment and attraction zones are the most important elements shaping the local urban spatial organization:

• Employment zones. The growing dissociation between the workplace and the residence is largely due to the success of motorized transport, notably the private automobile. Employment zones being located away from residential zones have contributed to an increase in number and length of commuting trips. Before suburbanization, public transit was wholly responsible for commuting. Today, the automobile supports the majority of these trips. This trend is particularly prevalent in highly populated, industrialized and urbanized zones, notably in North America and Western Europe, but motorization is also a dominant trend in developing countries.
• Attraction zones. Attraction zones linked to transport modes are areas to which a majority of the population travels for varied reasons such as shopping, professional services, education and leisure. As with central place theory, there is a certain hierarchy of services within an urban area ranging from the central business district offering a wide variety of specialized services to small local centers offering basic services such as groceries and personal banking.

The development of cities is conditioned by transport and several modes, from urban transit to the automobile, have contributed to the creation of urban landscapes. Three distinct phases can be noted:

• The conventional/classic city. Constructed for pedestrian interactions and constrained by them, the historic city it was compact and limited in size. The emergence of the first public transit systems in the 19th century permitted the extension of the city into new neighborhoods. However, pedestrian movements still accounted for the great majority of movements and the local spatial organization remained compact. Many European and Asian cities still have a significant level of compactness today.
• Suburbanization. The advent of more efficient public transit systems and later on of the automobile permitted an increased separation of basic urban functions (residential, industrial and commercial) and the resulting spatial specialization. The rapid expansion of urban areas that resulted, especially in North America, created a new spatial organization, less cohesive than before but still relatively adjacent to the existing urban fabric. Although this process started in the early 20th century, it accelerated after the Second World War.
• Exurbanization. Additional improvements in mobility favored urban expansion in the countryside where urban and rural activities are somewhat intermixed. Many cities became extended metropolitan regions, with a wide array of specialized functions including residential areas, commercial centers, industrial parks, logistics centers, recreational areas and high tech zones. These exurbanization developments have also been called "edge cities".

The automobile has clearly influenced the new spatial organization but other socioeconomic factors have also shaped urban development such as gentrification and the increase in land values. The diffusion of the automobile has lead to an urban explosion. The car has favored the mobility of individuals thus permitting a disorderly growth and an allocation of space between often conflicting urban functions (residential, industrial, commercial). Transport thus contributes to the local spatial organization, however, it must also adapt to urban morphologies. Transport networks and urban centers complement and condition each other.