Former steel mills and other industrial complexes are, in many areas of the United States, in a state of decay. Concerns about environmental hazards, for example, asbestos-covered buildings that must be torn down if development is to proceed, remain. Indeed, in areas where buildings are already collapsed or toxins have leached into the soil, cleanup is especially complicated.

In addition to being eyesores and environmental disaster zones, these neighborhoods store valuable space that, if rejuvenated, could help cities cope with demands for expansion.