Since the 1950s, myriad forces have expanded America's urban, metropolitan and megaregion development forms. Using a net worker exchange model, the geographic extent of commuter sheds is documented for 22 metropolitan areas within the continental United States. In addition to commuting patterns, county-to-county migration data provide collaborating evidence for the extent of metropolitan commuter sheds. Actual commuter sheds are significantly larger than the boundaries of Metropolitan Planning Organizations, created by the federal government to review and approve transportation investments in metropolitan areas. For contiguous metropolitan areas, criteria are suggested for recognizing Transportation Megaregions based on their role as global gateways and their potential for high-speed rail service. By gaining a better understanding of development patterns at urban, metropolitan and megaregion scales, the dissertation addresses ways to improve transportation governance. The focus of this study is not on the civil engineering aspects of transportation planning. Rather, the dissertation sets forth a new paradigm for transportation governance that includes scale-dependent decision-making and funding strategies. / Ph. D.