An arcology is distinguished from a merely large building in that it is designed to lessen the impact of human habitation on any given ecosystem. It could be self-sustainable, employing all or most of its own available resources for a comfortable life: power; climate control; food production; air and water conservation and purification; sewage treatment; etc. An arcology is designed to make it possible to supply those items for a large population. An arcology would supply and maintain its own municipal or urban infrastructures in order to operate and connect with other urban environments apart from its own. Arcology was proposed to reduce human impact on natural resources. Arcology designs might apply conventional building and civil engineering techniques in very large, but practical projects in order to achieve pedestrian economies of scale that have proven, post-automobile, to be difficult to achieve in other ways. Soleri describes ways of compacting city structures in three dimensions to combat two-dimensional urban sprawl, to economize on transportation and other energy uses. Like Wright, Soleri proposed changes in transportation, agriculture, and commerce. Soleri explored reductions in resource consumption and duplication, land reclamation; he also proposed to eliminate most private transportation. He advocated for greater "frugality" and favored greater use of shared social resources, including public transit (and public libraries).