What Data Set to Use for Our Transit Equity Project?

What demographic data sets will we use to compare against Transit Score to assess equity?

The 2000 Census is currently the only complete data set at the census tract level, so we’re going to start there. Obviously that’s way out of date and we shouldn’t reach any strong conclusions based on it.

I was asked in an earlier thread if ACS (American Community Survey) data was available at the tract level and I answered that it was. I was almost right. ACS is based on annual sampling (as opposed to the complete census that happens every 10 years) but features a longer questionnaire and therefore more data items.

In order to accumulate enough data points for areas as small as a census tract (a census tract has about 8,000 people, give or take several thousand), it takes five years of ACS sampling. ACS will release its first 5-year data set in December 2010, so at the point we would switch over and have much more current data. The 5-year data sets will then be updated annually (kind of a moving average) and that would likely be the preferred data set on an ongoing basis.

And on the mapping front, with the help of a KML file from TriMet, we’ve added the outline of the service district to the map. Our scoring process has finished Clackamas County and has now moved on into Multnomah County.

11 responses to “What Data Set to Use for Our Transit Equity Project?”

  1. So, I’m curious what it is that you’re offering with this project that hasn’t already been done? See, for example, the Equity Atlas created by the Coalition for a Livable Future, which includes a whole chapter (chapter 5) on transit equity, including a public transit score. http://www.equityatlas.org

    Sure, it’ll be nice when you update it to include ACS data, but the overall picture has long since been drawn….

  2. I’ve spoken with the CLF folks about this project and they’re supportive. There are a couple of key differences between what we’re doing and what’s in the Atlas:

    1) The Atlas gets updated at best every couple of years – for example I don’t think the current Atlas includes the Green Line. We can update our score every time TriMet does a service change.

    2) The Atlas is measuring walking distance to the nearest stop, with some kind of factor for frequent service as well. My belief is that Transit Score is a more sophisticated measure of your ‘reach’, i.e. do you have access to good transfers. MAX also gets much higher transit scores presumably because it’s faster to cover geography than local buses do. So I tentatively think it’s a better measure.

  3. I think it would be interesting to mash this up with density data. Is there really a equity issue if, perhaps, it turned out that a poor area with a low dwellings per acre number didn’t have any worse transit than the wealthy areas with similar densities?

  4. One reaction just from looking at the Transit Score data: inner NE and central SE are much less well-served by transit than the MLK/Lloyd city core. I don’t think it’s a coincidence that these have become bike havens.

    I wonder if bike use actually tends to be higher in transit-poor areas of the central city than in transit-rich ones. The low-car status of a household and the quality of transit service would be the independent variables, and mode choice (bike or transit?) would be the dependent one.

    Will you have a mechanism for archiving this, so we can compare equity levels at the current level of service to equity levels in 2015, after four more service adjustments? In my mind, TriMet’s self-scrutiny over service cut impacts sort of misses the forest for the trees.

  5. I went through a different entry point into TriMet but the request wound in the technology group that supports Bibiana. The developer indicated that this kind of stuff would eventually show up on developer.trimet.org (but is not there yet).

  6. Will you have a mechanism for archiving this…

    We’ll definitely take each scoring ‘snapshot’ and put it somewhere permanent (it’s essentially just going to be a spreadsheet).

  7. The zone boundaries aren’t exactly legally defined shapes like other areas are. This means that a property isn’t really within a certain zone; also it may have access to stops in multiple zones. Zones only come into play at transit routes. See the end of this document.

    Also, speaking about boundaries, one of the things I’ve been wanting to do is create a comparison of the TriMet, Metro, county, etc boundaries.

  8. How about we measure travel time from DOOR to DOOR with randomized start times.

    We could also measure total cost per mile traveled.

    And include ALL modes of transportation.


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