Updated: Transit Equity: Where Are You?


I am mortified. In the comments, Michael has identified a methodological error in the way I analyzed proximity to a regional center (downtown is after all, also a regional center). But in the process of re-computing those numbers, I discovered a computation error in my calculations for the system center, so both new correlation coefficients were incorrect, and my conclusion about poly-centrism unsupported…

Mea culpa… corrections below.

Original Post:

As promised, I’m continuing to add data to our transit equity data set. The latest addition is distance based – how far are you from a center.

The concept behind the Region 2040 plan is that we are going to become a poly-centric region. Portland’s central city will remain the center of the region, but we then also have 7 regional centers and a number of town centers. Housing, employment and services should cluster around each of these centers, reducing the need to travel long distances on a daily basis.

So today’s question is how strong is the effect of these centers on transit service? To figure this out, I calculated two distances for each block group:

1) The center of the block group to the ‘transit system center’ (I used SW 5th and Yamhill where all four LRT lines meet as my ‘system center’).
2) The center of the block group to the nearest regional center (I used the transit center in each regional center as that point, pulled from a TriMet data set on the CivicApps site).

Those columns have been added to our correlation data set spreadsheet.

The correlation results (negative because service decreases as you get further from a center):

  • Distance to system center: -0.58 -0.68
  • Distance to nearest regional center: -0.08 -0.48

By comparison, our correlation coefficient for density is 0.53, so distance from the system center is even more predictive of service level than density (although they certainly vary together to a strong degree – the correlation coefficient between density and distance from the center is 0.53).

The more significant finding is that the correlation for distance to a regional center is weak, our transit system is NOT very poly-centric yet. That shouldn’t surprise anyone, but it’s interesting to put a number on it. Unsupported by the revised data… In fact, the correlation with distance to a regional center rivals density as a reasonably strong correlation.

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