At the macro level, prescriptive IE seeks to rationalize aggregate materials and energy flows, which are strongly influenced by settlement patterns. Alberti (1999) uses four dimensions to characterize these patterns in her review of links between urban patterns and environmental performance: (a) urban form (degree of centralization or decentralization); (b) density (ratio of population or jobs to area); (c) grain (diversity of functional land uses such as residential and industrial); and (d) connectivity (extent of interrelation and availability of multiple modes of circulation for people and goods among local destinations). Her review of the empirical literature suggests the following tentative relationships:
• resource use per capita or job decreases with centralization, higher density, finer grain and higher connectivity;
• air pollution concentrations have an indeterminate relationship with urban form, density and grain, and they decrease as connectivity improves;
• water pollution concentrations have an indeterminate relationship with urban form, grain and connectivity, and they increase as density increases;
• habitat fragmentation decreases with centralization and higher densities but it increases with better connectivity;
• exposure of human populations to air pollutants increases with density, and its relationships to urban form, grain and connectivity are unknown.
Planning is a major point of leverage on urban patterns, and hence is an important point of entry for industrial ecologists seeking to reduce aggregate environmental impacts. Local planners can be encouraged to support compact, mixed-use developments that allow residents to substitute walking for driving on some daily trips, for example (Leccese and McCormick 1999). Higher governmental levels need equal attention, of course - a consensus list of the top 10 influences on the US metropolis during the last 50 years awards its top spots to the popularity of cars, the 1956 federal Interstate Highway Act and Federal Housing Administration mortgage regulations (Fishman 1999).
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