11.522: UIS Research Seminar (Fall 2014) - Discussion notes
Over the past few decades, transit-oriented development (TOD) has gained popularity as a more lively and walkable alternative to traditional car-dependent suburban neighborhoods. These developments emphasize a higher-density mix of commercial and residential uses within walking distance of a transit node. They are typically designed to enhance walkability through highly-connected street networks, pedestrian paths and other features that encourage circulation.
Given this promise, a number of studies have sought to establish a link between the physical form of a neighborhood and its degree of automobile dependence. This typically requires developing a metric of “neighborhood accessibility” based on a number of factors such as street layout and mix of uses. Authors also considered factors beyond the reach of an individual neighborhood, such as access to employment centers and transit. Armed with this metric, the studies looked at data from travel diaries to draw comparisons between different neighborhoods in terms of Vehicle Miles Travelled (VMT), number of trips and other travel measures. Early results were mixed and suggested a tenuous relationship at best. Yet, many of these studies suffered from aggregation problems that often resulted in an ecological fallacy. Authors also struggled with the problem of residential self-selection. It is difficult to determine whether a neighborhood has lower average VMT because of its physical characteristics or because people who inherently drive less prefer to live there. While the issue of self-selection still remains a problem, more disaggregated studies have demonstrated a stronger link between built form and transit that begs additional investigation.
Looking to the Future
Emerging technologies have the potential to dramatically change notions of neighborhood accessibility. For example, on-demand ride sharing may forge new connections between previously inaccessible neighborhoods that lack bus or transit service. This could impact the design of accessible neighborhoods and could upend the current emphasis on walkability and mixed use. Given that ride sharing reduces the need for parking, it could also enable a densification of the suburbs without the customary expansion in rapid transit.
Krizek’s paper provides an excellent review of literature and develops an approach that avoids many of the problems associated with previous studies. Using a longitudinal sample of families in the Seattle area, he compares the travel patterns of people who changed residence in association with a measure of neighborhood connectivity. In this way he attempts to deal with both aggregation problems and the issue of self-selection.
Susan Handy’s paper gives a good overview of the challenges involved in developing measures of neighborhood connectivity, particularly on a regional scale. She discusses some of the tradeoffs between increased precision and the costs of data collection, as well as the role of GIS.
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