Applying the CTOD Performance-based Typology
To the Reston TOD Jobs-Housing Balance Issue
In December 2010, the University of Maryland’s Center for Transit-Oriented Development (CTOD) published a comprehensive study of TOD areas focused on characterizing these developments by type and identifying normalized features. This analysis includes the approximately 3,760 existing transit station areas in 39 regions across the country, as reported in the CTOD’s National TOD Database. The study also contains a series of case studies for various TOD areas of different types and provides a model that can be used in developing plans for TOD areas.
The typology is organized around “performance-based TOD areas” that are segmented by (a) the balance between residential and employee populations, and (b) the performance-driving vehicle miles traveled (VMT). The typology breaks the balance dimension into three equal categories—residential, balanced, and employment. It segments the VMT dimension into five categories ranging from lowest to highest. This typology overlay is depicted as follows in the study (p. i):
Among its key findings in using this typology is the following regarding Urban Form (p. ii):
“Low VMT transit zones tend to have more intensity (residents + workers) and higher residential densities than high VMT transit zones. Residential densities in low VMT transit zones are over 15 times as high compared to high VMT transit zones. Additionally, transit zones have smaller block sizes.”
Later, the study explores the “normative” value of these various types of TOD places. It defines “normative” in this way (p. 14): “For the purpose of this Guidebook a Normative Metric is defined as a measure that allows for the comparison of similar transit zones within each place type. These
metrics are normative, in the sense that they represent the average value, of the universe of values, within each place type.” In brief, the normative value represents an average across the 3,760 existing TOD areas in the country for a particular balance/performance cell; it is not an aspirational goal or standard. In looking at the use of non-auto transportation, here are its results:
If a key goal is to reduce auto use in Reston TOD areas, that is, create an urban form near the bottom of the above graphic, then a residential urban form is the best urban form choice followed by a balanced urban form. An employment-dominated form—one in which the employee-resident ratio is 2:1 or greater (a jobs-housing balance of 4:1 or greater)—is the least likely to achieve the desired outcome of moving people out of their cars and in to public transit, biking, or walking. This nation-wide finding is exactly the same result demonstrated in the 2006 WMATA TOD area ridership survey which showed that residents of TOD areas had a greater propensity to use Metrorail than workers in TOD areas no matter what the distance from the station.
This overarching conclusion is reinforced strongly by looking one level deeper into CTOD’s data: What differences are there in commuting behavior of residents vs. incoming workers in public transit use at low VMT levels? Here are CTOD’s results:
In brief, these tables show that—in the lowest two levels of VMT—residents are likely to more-than-double their use of public transit as an area becomes more residential while workers’ behavior changes little, if not in the wrong direction. This suggests that any significant improvement in moving people in TOD areas out of their autos will most likely come from increasing the proportion of residents in a TOD area.
The CTOD study’s findings reinforce the correctness of RCA Reston 2020’s position that the populations of residents and workers in Reston’s TOD areas ought to be roughly equal and, in particular, the number of jobs should not exceed the number of residents. This roughly translates into a maximum jobs-housing balance of 2:1 under the assumptions currently used by the Reston Master Plan Special Study Task Force. If this standard is adopted as part of the Reston Master Plan for its TOD areas, it will go a long way to alleviating congestion growth and environmental damage as well as increasing Metrorail use and limiting needed investment in congestion-relieving improvements.
RCA Reston 2020 Committee
April 23, 2011
Performance-based Transit-Oriented Typology Guidebook, Center for Transit-Oriented Development, December 2010