The Land Use – Transport System

Urban areas are characterized by social, cultural, and economic activities taking place at separate locations forming an activity system. Some are routine activities, because they occur regularly and are thus predictable, such as commuting and shopping. There are also activities that tend to be irregular and shaped by lifestyle (e.g. sports and leisure) or by specific needs (e.g. healthcare). Such activities are usually related to the mobility of passengers. In addition, there are production activities that are related to manufacturing and distribution, whose linkages may be local, regional, or global. Such activities are usually associated with the mobility of freight. Since activities have a different location, their separation is a generator of movements of passengers and freight, which are supported by transportation. Therefore, transportation and land use are interrelated because of the locational and interactional nature of urban activities.

Most economic, social, or cultural activities imply a multitude of functions, such as production, consumption, and distribution. The urban land use is a highly heterogeneous space, and this heterogeneity is in part shaped by the transport system. There is a hierarchy in the distribution of urban activities where central areas have emerged because of economic (management and retail), political (seats of government), institutional (universities), or cultural factors (religious institutions). Central areas have a high level of spatial accumulation, and the corresponding land uses, such as retail. In contrast, peripheral areas have lower levels of accumulation corresponding to residential and warehousing areas.

The preferences of individuals, institutions, and firms have an imprint on land use in terms of their locational choice. The representation of this imprint requires a typology of land use, which can be formal or functional:

Formal land use representations are concerned with qualitative attributes of space such as its form, pattern, and aspect and are descriptive in nature.

Functional land use representations are concerned with the economic nature of activities such as production, consumption, residence, and transport, and are mainly a socioeconomic description of space.

At the global level, cities consume about 3% of the total landmass. Although the land use composition can vary considerably depending on the function of a city, residential land use is the most common, occupying between 65 and 75% of the footprint of a city. Commercial and industrial land uses occupy 5-15% and 15-25% of the footprint, respectively. There are also variations in the built-up areas that are commonly a function of density, level of automobile use, and planning practices. In automobile-dependent cities, 35 to 50% to land-use footprint is accounted for by roads and parking lots. Within a parking lot, about 40% of the surface is devoted to parking vehicles, while the remaining 60% is for circulation and access to individual parking spaces. These variations are the outcome of a combination of factors that reflect the unique geography, history, economy, and planning of each city.

Land use, both informal and functional representations, implies a set of relationships with other land uses. For instance, commercial land use involves relationships with its suppliers and customers. While relationships with suppliers will dominantly be related to the mobility of freight, relationships with customers would also include the mobility of people. Thus, a level of accessibility to both systems of circulation must be present for a functional transportation/land use system. Since each type of land use has its own specific mobility requirements, transportation is a factor of activity location.

Within an urban system, each activity occupies a suitable, but not necessarily optimal location, from which it derives rent. Transportation and land use interactions mostly consider the retroactive relationships between activities, which are land use related, and accessibility, which is transportation-related. These relationships have often been described as a classic “chicken-and-egg” problem since it is difficult to identify the cause of change; do transportation changes precede land-use changes or vice-versa? There is a scale effect at play in this relationship as large infrastructure projects tend to precede and trigger land-use changes. In contrast, small scale transportation projects tend to complement the existing land use pattern. Further, the expansion of urban land use takes place over various circumstances such as infilling (near the city center) or sprawl (far from the city center) and where transportation plays a different role in each case. For infilling, the value of land becomes high enough to justify developments despite potential congestion, while for sprawl, accessibility has improved enough to justify developments.

Urban transportation aims at supporting transport demands generated by the diversity of urban activities in a diversity of urban contexts. A key for understanding urban entities thus lies in the analysis of patterns and processes of the transport – land use system since the same processes may result in a different outcome. This system is highly complex and involves several relationships between the transport system, spatial interactions, and land use:

·         Transport system. The transport infrastructures and modes that support the mobility of passengers and freight. It generally expresses the level of accessibility.

·         Spatial interactions. The nature, extent, origins, and destinations of the urban mobility of passengers and freight. They take into consideration the attributes of the transport system as well as the land use factors that are generating and attracting movements.

·         Land use. The level of spatial accumulation of activities and their associated levels of mobility requirements. Land use is commonly linked with demographic and economic attributes.

A conundrum concerns the difficulties of linking a specific transportation mode with specific land use patterns. While public transit systems tend to be associated with higher densities of residential and commercial activities and highways with lower densities, the multiplicity of modes available in urban areas, including freight distribution, conveys an unclear and complex relationship. Further, land use is commonly subject to zoning restrictions in terms of the type of activities that can be built as well as their density. Therefore, land use dynamics are influenced by planning restrictions and the urban governance structure.