Transportation, Land Use and the Environment

Author: Dr. Jean-Paul Rodrigue

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1. Land Requirement and Consumption

The main impact of urbanization processes 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 superior to 5,000 square km. Such large cities obviously cannot be supported without a vast and complex transport system, and 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 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 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 to the point that the notion of cities was replaced by the notion of metropolitan areas and urban regions oriented along corridors. With the rationalization of urbanization, the rationalization of transportation has allowed the reclamation of vast amounts of land from rural activities towards other usage. The duplication and generalization of infrastructure, public and private alike, have resulted in supplementary land requirements. 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 geographical growth of cities has not been proportional to the growth of population, resulting in lower densities and higher waste of space. 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, 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 have impacts of 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.
• 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.
• Spatial interaction. Refers to the nature and the structure of movements generated by urban land uses.

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.

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 services at an efficient cost.

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. 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" state. 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.

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 per passenger km
	Infrastructure	Road density
		Public utilities provision costs
Social Costs	Community disruption	Environmental externalities
		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. We must also consider that the function of land use contributes to environmental degradation as a source of waste, particularly for industrial land uses (air pollution, water pollution, hazardous materials, etc.).