Chicago is Rural: The Inconsistencies and Absurdities of Street Connectivity Indices
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Many contemporary urban design metrics have been developed to quantify the connectivity of street networks. Municipalities and other authorities are beginning to realize the important characteristics of fine-grained street networks including street frontage, route options, and land use accommodation. The different metrics to describe these characteristics have been discussed extensively in Susan Handy’s book Planning for Street Connectivity: Getting from Here to There (2003). Of these metrics, many are of a variety referred to as a connectivity index. Connectivity indices attempt to distill the relative urban attributes of a street network into a ratio of street links to intersection nodes. If successful, this would prove an easy and efficient way to insure that future streets are developed with some minimum standard of block size and overall connectivity. However, as this paper will show connectivity indices have many internal flaws that render them ultimately inconsistent and ineffective. One of these metrics, in fact, gives downtown Chicago’s street network a “rural” reading. There are many versions of connectivity indices that can be found across the US. Three versions will be discussed in this paper from three different sources: the Virginia Department of Transportation; Cary, North Carolina; and Kannapolis, North Carolina. Each connectivity index utilizes the exact same ratio of street links over intersection nodes; however, the exact methods used to calculate the ratio varies. Figure 1 displays the three methods for counting nodes and links that will be studied in this paper.