Assessing the measures of street connectivity: A comparative study of the largest American cities

Abstract

The thesis offers a systematic characterization of the morphology of street networks in metropolitan areas in the United States in order to help assess current conditions. Measures of street connectivity, particularly those of road segment length, block area, metric reach and directional distance, are measured for all road segments within each of the 24 largest Metropolitan Statistical Areas in the U.S. In order to characterize local areas within each MSA, these measures are also studied for a stratified sample of more than 4,500 local areas, each two miles in diameter, chosen at varying distances from the metropolitan center. As a point of comparison, a smaller sample of ninety-six local areas is chosen to illustrate distinctive street network types identified and discussed in the existing literature on urban morphology and street connectivity. This smaller typological sample provides benchmarks then for the characterization of the much larger random sample of local areas. The thesis profiles the variation both between and within the local areas of these metropolitan areas. In the face of the prevailing variability on street network types, the thesis also examines which measures of street connectivity best capture significant differences and, by implication, might be most effective in assessing street connectivity in the context of policy development and planning for possible urban development. The thesis concludes that the measure of 'metric reach,' which captures the street network length accessible within a specified network distance from any given point, used on its own, is a more sensitive descriptor of street connectivity than some of the measures more traditionally used, such as the distance between, or the density of, intersections. Metric reach also provides the most consistent characterization of trends such as the reduction of street network density within increasing distances from the historic city center, or the identification of polynucleated centers at varying distances from that center, whether these emerge as recently grown edge cities, or survive as centers of old towns absorbed into the expanding urban fabric.