It will be no surprise to our readers to hear that that there are some in the community who believe that our transit system has become less equitable in recent years as light-rail openings and budget-driven bus cutbacks create a perception of different service for different parts of the community.
But is that accurate? Light rail certainly does not exclusively serve affluent neighborhoods. Can we find a way to get past the anecdotes and accusations and actually quantify who’s getting served how well by TriMet?
We have a new tool to help with this. As we discussed last month, Transit Score is now available. It’s a new tool, and it may not be perfect, but it gives us an easy-to-comprehend number that’s objective (at least it’s not derived by anyone with a view about transit operations here in our region).
So how do we propose to make use of Transit Score to answer our equity question? We plan to:
1) Aggregate a Transit Score for every census tract in the TriMet service area (there are 286!).
2) Correlate those tract-level scores with other information about the census tracts like income, ethnicity, density and potentially other factors.
We’ll do this whole process in an open way, so anyone who’s interested can look over our shoulders and verify our data, or come up with their own alternative analysis.
The rest of this post will be about how we’re accomplishing step one – coming up with an aggregated transit score for a census tract.
The approach we’re using is to lay down a grid (about 1/4 mile) across each census tract, then use a geocoding service to snap each grid point to the nearest intersection. This keeps us from calculating a transit score for a corn field, and also eliminates redundancy in less dense parts of the street network. Depending on the census tract, we wind up with a half dozen to a couple of hundred points in the tract. An example of such a set of points is shown below.
In the next step, we’ll get Transit Scores for each of those points – we have over 11,000 to get – and compute averages for each tract. More about that, and how you can help, tomorrow…