SOCIAL VULNERABILITY ANALYSIS OF BQX & TRIBORO RX

New York, NY

By Nathaniel Jones
transit, planning, vulnerability, nyc

A spatial analysis of two proposed NYC transit projects (the BQX Streetcar & Triboro RX Rail Line) against the CDC's social vulnerability index.

This project started with a curiosity about possible points of comparison between two proposed NYC transit projects - the BQX Streetcar and the Triboro RX Rail Line. Both the BQX and the Triboro RX represent expensive, multiyear planning decisions for NYC. Both appear to serve somewhat similar purposes - including providing greater connectivity between NYC’s outer boroughs. Yet discussions of each alternative seem to be happening in a vacuum and there was a paucity of interactive maps comparing the projects. From a public policy decision-making perspective, I was interested in exploring non-traditional criteria for assessing the value of the projects, ultimately settling upon the Centers for Disease Control’s (CDC) Social Vulnerability Index (SVI).

As shown in the image above, levels of vulnerability vary across the city from low (green, and a value of 0) to high (red, and a value of 1). I decided to focus my map upon exploring how the BQX and Triboro RX routes and stops would serve NYC residents from a vulnerability perspective. After obtaining various public data layers for existing NYC transit options (subway, bus, ferry) and adding them to a basemap, I layered on the proposed routes of the BQX and Triboro RX (either obtaining public information or creating spatial data from available static images) and then added the CDC’s SVI polygon data layer. The SVI uses U.S. Census data to determine the social vulnerability of every census tract. The SVI ranks each tract on 15 social factors, including poverty, lack of vehicle access, and crowded housing, and groups them into four related themes. Each tract receives an overall vulnerability ranking, which I used as the basis for my analysis.

I prepared queries to identify the census tracts from the SVI layer that were located within 2000 feet of a proposed stop on either the BQX or Triboro RX route. Note: American urban planners conventionally assume that people will walk about a half-mile to a train station (i.e. 2640 feet). To account for the variability in size of the census tracks, 2,000 feet was used as the buffer for the intersect with the SVI layer. The results of this method can be seen in the image above, which shows the social vulnerability of tracts for the Triboro RX. I was interested in quantifying this visual, so I prepared queries to remove bad data (-999 values for non-populated areas like parks) and to calculate a population-weighted average level of social vulnerability for the route as a whole. I then carried out the same exercise for the BQX. My hypothesis was that the BQX, with a proposed route along the recently gentrified East River waterfront of Brooklyn, would contain a population that is less vulnerable than residents along the proposed route of the Triboro RX (extending from the bronx through more outlying areas of Queens and Brooklyn).

I added the results of my data analysis to a sidebar (as shown above). My analysis of the proposed routes of the BQX and Triboro RX finds that the SVI (weighted by population) is higher for the Triboro RX (0.747) than the BQX (0.487). This indicates that the likely beneficiaries of the proposed BQX are 53.4% less vulnerable than the likely beneficiaries of the proposed Triboro RX.

Finally, I added some interactive elements to the map to make it more engaging, including pop-ups of the vulnerability of specific census tracts, and the ability to draw your own mass transit route on the map and see how it would score against the vulnerability index (as shown above). I also gave page visitors the ability to submit feedback via a Google Form, which might yield interesting observations and sentiments from the general public.

Ultimately, transit planning decisions are multi-faceted and complex affairs considering many factors for evaluating costs and benefits in the course of making siting decisions. However, vulnerability indicators may represent an under-examined and fruitful avenue of exploration for public policy advocates and practitioners interested in connecting public investments to helping the most vulnerable members of a community. In the context of the BQX and Triboro RX, planners should at least consider the relative social vulnerability profiles of each proposed project before making funding decisions.