News

PSAP Update Webinar Videos and Slides

PSAP Update Webinar had been held on Oct. 24, 2018. For the video and presentation slides, please click here.


Federal Register notice of proposed criteria for  Census Block Groups, Census County Divisions and Equivalent Entities, Census Designated Places, and Census Tracts: https://www.federalregister.gov/documents/2018/02/15 

  • Responses due May 16, 2018

The webinar held on April 3, 2018 explained proposed criteria and responses. For more information, please visit here

CTPP Policy Change Announcement


MEMORANDUM

Date: January 4, 2018 (UPDATE: February 22, 2018)
To: CTPP Users
From: Census Transportation Planning Products program oversight board
Subject: Policy Change Announcement on Small and custom Geography in CTPP

Census Transportation Planning Products (CTPP) Oversight Board Discontinuing Census Transportation Analysis Zone (TAZ) for Small Geography Data Reporting, Adopting Standard Census Block Group. Urging the Transportation Planning Community to Engage in 2020 Census Participant Statistical Areas Program (PSAP)

WHO NEEDS TO SEE THIS MEMO?

MPOs, state DOTs, anyone who uses CTPP data by census TAZ and census TAD, Demographers, Travel Demand Modelers, Planners, GIS Specialists.

WHAT IS HAPPENING?

Following the release of the Census Transportation Planning Products (CTPP) 2012-2016 dataset in early 2019, the Oversight Board to the CTPP Program is announcing it will no longer include Transportation Analysis Zone (TAZ) and Transportation Analysis District (TAD) geographies in future requests for special tabulations of the U.S. Census Bureau’s American Community Survey (ACS) data. Future CTPP special tabulation requests will include the standard census block group geography instead.

Census TAZs are the component geographies of census TADs. As a result of discontinuing support for zonal level tabulations it is necessary to discontinue district level tabulations as well.

Currently the smallest standard census geography in the CTPP tabulation is census tract, which will continue to be reported, along with larger geographies such as state, county, minor civil division (MCD)[1], metropolitan statistical area (MSA), public use micro area (PUMA), urbanized area[2], and census designated place.  For more information, or with questions and comments, contact Penelope Weinberger, AASHTO’s Transportation Data Program Manager, at pweinberger@aashto.org

WHY WILL CTPP DISCONTINUE CENSUS TAZ?

The CTPP Board decided to request data at the census block group because of not only data quality and usability concerns but also to use resources more effectively. Since shifting from a decennial-based CTPP tabulation to an ACS-based tabulation, the smaller sample size found in the ACS has increased margins of error in the data at all geographic levels—usually to an acceptable degree. Typically, data quality decreases when smaller geographies are selected. Introducing non-standard census geographies further diminishes data quality because, generally, the population distribution—and consequently, sample distribution—has greater variation than in standard geographies. So, while data users should still be discerning about use of the smaller block group geography or the larger census tract, block group data generally will contain lower sample error than the current census TAZs.

Additionally, many areas of the country struggle to use CTPP data at the census TAZ level because it does not align with the TAZs found in their travel model.

Furthermore, the Census Bureau estimates that a 2020 Census TAZ Delineation Program would exceed $2.5 million, which would comprise more than half the CTPP Program 5-year budget. In addition, non-standard geographies are disproportionately more expensive to tabulate than standard geographies—resulting in higher costs for lesser quality data.

HOW CAN WE PREPARE FOR THIS CHANGE?

To best adapt to this change, the Board urges travel demand modelers, MPOs, state DOTs, and anyone who uses CTPP data by census TAZ and census TAD to participate in the 2020 Census Participant Statistical Areas Program (PSAP), and through it, adjust their census block group boundaries to better align with their model TAZ geographies. PSAP is the means for updating local census block group delineations, in addition to census tracts, census designated places, census county divisions, and various tribal geographies.

PSAP occurs in the lead-up period to the decennial census. If census block groups and local model TAZ boundaries gain better alignment through PSAP, generating both standard ACS and CTPP tables would be a more effective use of Bureau resources—maximizing data quality and usability by reporting at geographies relevant to transportation planners.

The PSAP guidelines will be published in the Federal Register in March of 2018, with a limited comment period for PSAP participants to communicate how the delineation process can best meet their needs. From now until May 2018, agencies can inquire about participation as noted below. PSAP invitation materials will be sent in July 2018 and the PSAP delineation phase will run from January to June 2019. PSAP verification will run from January to March 2020. In the coming months, to support the CTPP user community, the CTPP Board will be providing resources such as webinars and publications giving guidance and strategies to help agencies better align their block group and model TAZ geographies. Expect to see announcements and discussions on the CTPP listserv. More information below.

The CTPP Board wishes to get this message out now to give the CTPP user community as much time as possible to strategize and make plans for PSAP participation. The following is a list of things you and your agency can do to ensure success in this transition:

  • Get the word out by forwarding this message to as many contacts as possible.
  • Read the Federal Register’s notice on PSAP (published February 15, 2018) and submit comments based on your agency’s needs, until May 16, 2018. https://www.federalregister.gov/documents/2018/02/15  
  • Receive announcements and join the discussion of this change and other things important to the CTPP user community on our listserv: http://www.chrispy.net/mailman/listinfo/ctpp-news
  • Get in touch with your reps at your state data center(s) and let them know you want to be involved. https://www.census.gov/about/partners/sdc/member-network.html
  • Find out who in your area has participated in PSAP in previous decennial censuses. Contact the Census Bureau to let them know you want to participate in the 2020 PSAP and ask for information on who traditionally has participated in previous PSAPs in your area. Contact geo.psap@census.gov.
  • Reach out to traditional PSAP participants and let them know you want to play a role in this cycle. Start meeting so that you can begin to understand each other’s needs and the benefits of working together. The PSAP and TAZ Delineation Program have been two separate labor-intensive processes in the past. Consolidating into one program has the advantage of pooling limited resources into a collective effort.
  • Conduct an initial assessment of how your model TAZs and block groups do and do not align. Think through your agency’s travel model geography needs and how you would like PSAP to meet those needs.
  • Read through the initial guidance below on aligning block groups to model TAZ boundaries through PSAP.

INITIAL GUIDANCE ON ALIGNING BLOCK GROUPS AND MODEL TAZS THROUGH PSAP

Through conversations with the Census Bureau, and based on past PSAP efforts, the Board is providing some initial guidance on how the block group delineation process will likely work. This is subject to change, especially in response to comments submitted during the PSAP Federal Register public comment period; however, the following is what we anticipate:

  • Unlike census tracts, which the Census Bureau likes to preserve for time series analysis by a standard geography, block group boundaries are malleable, if they nest within census tracts and adhere to rules explained below.
  • On average, a block group is the size of a census TAZ and the national count of each geography is similar.
  • Even if agencies cannot redraw block groups as a one-to-one relationship with their model TAZs, two or more model TAZs could nest within a block group and receive the same distribution of attributes (e.g. 0, 1, 2, and 3+ vehicle households) as found in its parent block group geography.
  • There also could be cases where multiple block groups nest within one model TAZ and their aggregated attributes could be assigned to that TAZ.
  • A minimum threshold of 600 residents are meant to comprise a block group. For a census tract, the thresholds double–in this case a population of 1200.
  • The Geographic Update Partnership Software (GUPS) that the Census Bureau distributes for use in PSAP will flag the draft block groups that fall short of 600 people, based on the census block populations from the 2010 Census.
  • Flagged geographies will either need to be aggregated to exceed 600 residents, or the agency needs to provide a justification of why it is short of the resident threshold according to 2010 data. This justification can take many forms, such as:
    • More recent data shows that that geography has exceeded the 600-person threshold.
    • By 2020, your data shows that geography will exceed 600 residents.
    • If current or future estimates of population are not available, households and or units could be a substitute. A minimum threshold of 240 dwelling units or households (or something in that realm) will likely be used as a 600-residents equivalent.
    • The area is a special use area – like employment district or parkland.
      • If a geography has little to no residents because it is a commercial area, employment can be used for delineation. A minimum threshold of 600 jobs (or something higher) may be found in later guidance as an employment threshold.
      • An area with no population or jobs, such as a parkland area, may also qualify as a special block group.
  • The PSAP process provides an opportunity for agencies to give the Census Bureau boundary files by which they want block groups (and later, census blocks) split. These can be political boundaries, natural features, or transportation infrastructure.
  • New census block delineations used for reporting 2020 Census results will be determined through the 2020 Census Redistricting Data Program.

 

[1] In 12 MCD reliant states

[2] For Part 1: Residence tables