Measuring Equitable Development Opportunity
Using Census Data (ACS 2011-2015) from all the Block Groups in Boston, we defined the following variables shown in Table 1 to measure equitable development opportunities:
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Table 1: Equitable Development Opportunity Variables
Considering that next to housing, transportation is the second highest household cost, and that those households who use transit more tend to have lower overall transportation costs, we decided that those block groups with high percent of low income households (less than $50,000), and those more cost-burdened, should have a higher score (Reconnecting America, 2007; Schwartz & Wilson, 2006). It is also important to consider that the city of Boston (2015) defines its threshold for very low income households as those at 50% of the Area Median Income or AMI. In 2015, the AMI for a 4-person household in Boston was calculated at $98,500, thus, families with an income of less than $50,000 fit our purpose.
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Additionally, in terms of population density, it is known that to be most effective, transit-oriented development should be placed in areas with sufficient population density (Williams, 2008, p. 310). In addition, a population density threshold of 13 residents per acre (or 8,320 persons per square mile) is a significant threshold for mode choice (Cervero & Kockelman, 1997). However, since we are studying existing transit-rich areas, we defined that the lower the density, the higher the opportunity for new developments. Finally, renters have a higher transit use than the average American (Pollack, Bluestone, Billingham, 2010, p. 3); therefore, granting a higher score to these areas is appropriate.
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To determine the limits of each category (1 through 5), we looked at the statistical distribution of each variable across Boston and divided the information into 5 equal categories (20, 40, 60, 80, 100 percentiles). We used information on all of the city’s Block Groups in order to be able to compare between study areas and within study areas.
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Please find the intervals defined to score each block group in our study areas on Table 2.
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Table 2: Scoring Scheme
Once we defined the intervals to score the variables, the following step is to assign an average score in terms of the opportunity for equitable development to each block group. To do that, we used the ranges defined earlier to score each variable. The score for each block group is achieved by adding the results for each variable and then getting the average number. Please examine tables 3 and 4 to view an illustrative example of this process.
Table 3: Illustrative example block group values
Table 4: Illustrative example to view the final score of a block group.
The next step is to get a final score for each buffer area (0.5 miles around each transit station), which corresponds to the average of the scores of all the block groups that comprise it. The example below shows the average equitable development score of the block groups surround the Roxbury Crossing T Station.
