Methods of requiring ‘connectivity’ differ

Communities are choosing among more than one method when they set out to connect streets more thoroughly. The most prevalent method involves setting a few common-sense rules — limiting the lengths of blocks, prohibiting gated subdivisions, restricting or eliminating the construction of cul-de-sacs, and requiring streets that extend into adjacent areas when those tracts develop later. An alternative method — more complicated and problematical — is the use of a “connectivity index.” When governments regulate how long the blocks may be, “typical block length requirements fall in the range of 300 to 600 feet (although a few cities allow substantially longer blocks, at least under certain circumstances),” Susan Handy, Robert G. Paterson, and Kent Butler write in their admirably thorough study, Planning for Street Connectivity. “Cul-de-sacs are usually restricted to 200 to 300 feet and are allowed only in places where connections would be impractical.” Requirements of this sort seem to work well. “The block length approach is easily visualized and understood by developers and residents, and it produces a relatively predictable and evenly distributed network of streets,” the authors say. Localities vary in how they pursue this method. In Portland, Oregon, streets must be no more than 530 feet apart except where physical conditions make that impossible. In Portland’s highest-density, mixed-use areas, connections are to be less than 330 feet apart. Fort Collins, Colorado, prohibits gated developments and defines the maximum block size as seven to 12 acres, depending on the zoning. The code requires a four-way intersection every 1,320 feet along arterial streets, and requires more limited intersections every 660 feet between four-way collector or local street intersections. Communities should anticipate how a subdivision currently seeking municipal approval will link up to neighboring areas not yet scheduled for development. In the Portland area, cities and counties must prepare maps of potential future street connections to meet the metropolitan government’s standards. Communities have found that it’s a good idea to post signs on “stub” streets, notifying residents that when development occurs in the area beyond, the street will be extended, generating additional traffic. Otherwise, people may buy houses without realizing that they’re on what will eventually be a through street. Communities such as Cary, North Carolina, Middletown, Delaware, and Orlando, Florida, have devised connectivity indexes. One of the purposes of an index is to give developers the flexibility to respond to challenges posed by steep hills or other difficult topography. Cary’s connectivity index divides the number of street “links” (sections of street between intersections, including cul-de-sacs) by the number of street “nodes” (intersections and cul-de-sacs). This produces an index figure. If the figure is at least 1.2, Cary considers the development adequately connected. But to judge from a Street Connectivity map of a tract that would win approval under Cary’s system, the results are a farce. The Cary subdivision is unmitigated sprawl; it does not make walking or driving efficient, yet its 1.22 rating allows it to win approval. Other communities have required higher index figures. Even so, such a system is troubling. Connectivity indexes are difficult for the public to understand, and they “can complicate planners’ attempts to educate local officials, citizens, and developers about the importance of connectivity,” Street Connectivity’s authors acknowledge. Although the book does not dismiss such indexes, Handy told New Urban News, “I think there is a real question about [their] effectiveness” Few, she said, seem to address how well a development is linked to adjacent neighborhoods — as opposed to having reasonable internal connections. “If the neighborhood is still not well connected to surrounding development,” Handy said, “then it’s not likely to have much impact on travel behavior.” u