Transportation, Land Use and the Environment

Author: Dr. Jean-Paul Rodrigue

1. Land Requirement and Consumption

The main impact of urbanization has been the expansion of urban land use, which means that a large city of 5 million inhabitants may stretch over 100 km (including suburbs and satellite cities) and may use an amount of land exceeding 5,000 square km. Such large cities obviously cannot be supported without a vast and complex transport system. Also, modal choice have an important impact on land consumption. The preference for road transportation has led to a massive consumption of space with 1.5 to 2.0% of the world's total land surface devoted to the automobile, mainly for roads and parking lots. The dependence on transportation has reached a point where 30 to 60% of urban areas are taken by road transportation infrastructure alone. In more extreme cases of dependency on road transportation, such as Los Angeles, this figure can reach 70%. Yet, for many developing countries such as China and India, motorization is still in its early stages. For China to have a level of motorization similar to those of Western Europe would imply a fleet of vehicle superior to the current global fleet. From a land requirement perspective, motorization would thus be a technical impossibility.

The size of cities takes large quantities of land and their growth lead to the notion of metropolitan areas and, further, urban regions oriented along corridors. With urbanization, the expansion of transportation has allowed the reclamation of vast amounts of land from rural activities towards other usage. Also, the duplication and generalization of infrastructure, public and private alike, have resulted in supplementary land requirements. This is notably the case for large transport terminals such as ports and airports where several were built because they belonged to different administrative jurisdictions. The general aim was to convey a high level of accessibility to answer mobility demand of vast areas. While in several regions road transportation infrastructures are overused, a situation of over-capacity exists in others. The formation of compact and accessible cities must be allowed to contend with the already existing built environment while considering several limits to development and urban renewal through temporal constraints and common limitations in capital availability.

The geographical growth of cities has not been proportional to the growth of population, resulting in lower densities and higher space consumption. This also applies to manufacturing and freight distribution activities that tend to expand horizontally with the expansion of the transportation and storage functions, particularly for distribution centers. Such phenomena have not occurred in the same fashion and in the same proportion around the world. An increase in the quantity of energy consumed and waste generated has been the outcome. A typical city of one million inhabitants in an developed country daily consumes 600,000 tons of water, 10,000 tons of fuel and 2,000 tons of food, leading to a daily output of 500,000 tons of sewage, 2,000 tons of refuse and 1,000 tons of air pollutants (mainly CO2 and NO2). Consequently, changes in urban land use and its transport system have aggravated the environmental impacts of cities.

2. Spatial Form, Pattern and Interaction

The structure of urban land use has an important impact over transport demand and over the capacity of transportation systems to answer such needs. This involves three dimensions, which influence the environmental impacts of transportation and land use:

Spatial form. Refers to the spatial arrangement of a city, particularly in terms of the orientation of its main axis of circulation. This form thus conveys a general structure to urban transportation ranging from centralized to distributed. The prevailing influence has been expansion and motorization, resulting in polycentric cities, which are economically and functionally flexible but consume more energy.
Spatial pattern. Refers to the organization of the land use in terms of location of major socio-economic functions such as residence, commercial and industrial. The prevailing trend has been a growing disconnection and fragmentation between land uses. Also, different types of land use can be incompatible with their adjacency the source of additional externalities. For instance, residential land use is incompatible to the majority of industrial, manufacturing, warehousing and terminal activities activities as they generate noise and congestion externalities to which residents are highly susceptible. In such a context, buffers, which apply different barriers effects to promote physical separation, can be used to help mitigate incompatible land uses.
Spatial interaction. Refers to the nature and the structure of movements generated by urban land uses. The prevailing trend has been a growth in urban interactions in terms of their volume, complexity and average distance.

The spatial location of activities like residence, work, shopping, production and consumption give some indications on the required travel demand and average distances between activities. With a tendency towards specialized land use functions and thus a spatial segregation between economic activities, interactions are proportionally increasing. It is over the matter of density that the relationships between transportation, land use and the environment can be the most succinctly expressed. The higher the level of density the lower the level of energy consumption per capita and the relative environmental impacts. Around the world, a remarkable diversity of urban densities is found, a complexity compounded by how this density changes in relation to the city center.

Paradoxically, the outward expansion of cities and suburbanization has favored a relative uniform distribution of land use densities, notably in cities with a previously low density level. In recent decades, the average density of several large metropolitan areas has declined by at least 25% implying additional transport requirement to support growing mobility demands often related to lower densities. Further, residence / work separation is becoming more acute as well as the average commuting distance. For instance, in the American context the average commuting time has climbed from 21.7 minutes in 1980, to 22.4 minutes in 1990 and 26.5 minutes in 2003. It is consequently increasingly difficult to provide a variety of urban transit services at an efficient cost.

A higher level of integration between transportation and land use often results in increasing levels of accessibility without necessarily increasing the need for automobile travel. The slow transformation of urban land uses, with annual rates lower than 2%, makes it difficult to establish sound transportation / land use strategies that could have effective impacts over a short period. As it is generally market forces that shape such changes, it is uncertain which change would have the most significant impact on urban land use. Since it took 30 to 50 years to North American, Australian and to some extent European cities to reach their current patterns, it may take the same amount of time to reach a new equilibrium. Energy prices, particularly petroleum, are likely to be the most significant forces shaping urban development. Consequently, the environmental impacts of transportation and land use are likely to stay prevalent in the urban context for several decades.

3. Environmental Externalities of Land Use

Land use, as a spatial structure, is linked to a number of externalities. Strategic indicators that are recurrent involve VMT (vehicle-mile traveled), transit ridership and average commuting distance to the workplace, which are all spatial interactions variables.

Land Use Externalities
Type	Field	Possible Measures
Economic Costs	Urban pattern and density	Average commuting distance
		Density of population
		Decrease in agricultural production
	Energy	Gasoline use per capita
	Energy	Energy per passenger km
	Infrastructure	Road density
	Infrastructure	Public utilities provision costs
Social Costs	Community disruption	Environmental externalities (e.g. noise)
Social Costs	Community disruption	Accessibility to facilities
Environmental Costs	Damage to the ecosystem	Land taken to the natural environment

Economic Costs. They are related to the costs incurred to maintain an urban area according to the characteristics of its land uses. Lower densities and segregated land uses increase economic costs in terms of average commuting distances, public utility provision, and energy consumption. In several instances, urban growth has always occurred at the expense of the most productive rural areas. Once land use shifts from rural to urban, it rarely becomes available for other usage. High levels of subsidies for urban transit are an indirect externality related to land use. It is increasingly difficult to provide adequate levels of service, notably in suburban areas, where land use density (residential and commercial) is not high enough for a profitable public transit system. Overall, land use externalities affect the economic efficiency of urban areas.
Social Costs. Community disruption includes a wide range of social cost imposed by the land use density, pattern and interaction. Environmental externalities, like noise, smog and odors, contribute to disrupt the quality of life. Transportation infrastructure, notably railways and highways are a physical barrier that divides a community and disrupt pedestrian / vehicular linkages. Further, the design of the transportation system for a specific mode restrains accessibility of persons who do not have access to that mode. This is notably true with cars.
Environmental Costs. The most obvious environmental cost is related to the quantity of land taken at the expense of the natural environment. It must also be considered that land use contributes to environmental degradation as a source of waste, particularly for industrial activities (air pollution, water pollution, hazardous materials, etc.).

In several instances, the environmental externalities imposed by existing and emerging land use patterns impose significant economic, social and environmental costs that communities are less willing the assume. This has led to various land use regulations, mostly under the umbrella of "smart growth" initiatives.

Higher energy prices are likely to shape urban development towards a dynamic that is more conventional and where distance decay plays an active role. The last half a century has been associated with a declining role of public transit, a more disorganized spatial structure and the prevalence of suburbanization. This trend could be reversed with two possible and interdependent paths of land use changes unfolding, depending upon the concerned urban setting:

Densification. Involves a more rational and intensive use of the existing land uses to minimize the environmental footprint and the level of energy consumption. Yet this implies higher levels of capital investment and the provision of an adequate level of public transit, since in a car-dependent context densification easily leads to congestion and other externalities.
Devolution. Due to economic and demographic trends several cities could lose a share of their population, imposing a rationalization of urban land uses. In old industrial regions of Europe and North America, several cities have lost a share of their economic base and correspondingly their population. This involves dismantling urban infrastructure and closing sections or whole neighborhoods, which could lead in time to the emergence of urban forests and even forms of urban agriculture. Detroit is a salient example since the population of the city dropped by more than a half from 1.8 million in 1950 to 713,000 in 2010. Yet, the population of its metropolitan area has remained relatively stable since the 1970s, hovering around 4.2 million. This implies that the process of devolution is very location specific.