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Using 5-year ACS for Transportation Planning Applications

Using 5-year ACS for Transportation Planning Applications. Elaine Murakami FHWA Office of Planning Elaine.murakami@dot.gov 206-220-4460 (in Seattle). The journey to work is still relevant. About 20% of Person Miles of Travel (and 27% of VMT) is Commuting Labor force participation rate:

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Using 5-year ACS for Transportation Planning Applications

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  1. Using 5-year ACS for Transportation Planning Applications Elaine Murakami FHWA Office of Planning Elaine.murakami@dot.gov 206-220-4460 (in Seattle)

  2. The journey to work is still relevant • About 20% of Person Miles of Travel (and 27% of VMT) is Commuting • Labor force participation rate: • 74% men • 62% women To/from work

  3. Commuting is key factor in congestion

  4. Census Transportation Planning Products • Nationwide, customized tabulation for the transportation community • First completed in 1970 (not nationwide), with subsequent packages in 1980, 1990, and 2000. • Previously used decennial long form, now using ACS. • Includes home-to-work flow

  5. CTPP: 3-year and 5-year • Received 3-year (2006-2008) from CB, and AASHTO (Beyond 2020) working to post on web • Travel demand model calibration and validation • Analysis of transit major investments • 5-year (2006-2010) due in 2012 • Use of Census 2010 results to adjust weights n the Population Controls • Requires implementation of new disclosure avoidance (“masking”) techniques.

  6. Methods to protect individual confidentiality already in place with ACS records • Small sample • Data switching • Imputation • High for income (13%) • High for place of work (20+%) • Rounding for custom/special tabulations

  7. Census Bureau Disclosure Review Board: Rules for the CTPP 5-year tab • Cell Means and aggregates require 3 unweighted records • For Pt 3 (flow), 3 unweighted records for each table, each cell, with the exception of the 1-way MOT table. • 3 unweighted records for the marginals in any cross-tabulation with MOT.

  8. :How many ACS records per tract or TAZ after 5 years of ACS data accumulation? RESULT of this number of unweighted records with the DRB rules  LOTS OF SUPPRESSSION

  9. What tables should be in the CTPP? • Reduce the # of variables cross-tabbed with variable “Means of Transportation” • Reduced from 17 to 5 for the 3-year list. • Keep the reduced list of 5 cross-tabs • Collapse the categories – reduce the total # of cells in each table. • Use data synthesis methods (now using term “masking”)

  10. NCHRP 08-79: “Producing Transportation Data Products from the ACS that Comply With Disclosure Rules NCHRP is funded by State DOTs SP&R • Project schedule: Jan 2010-July 2011 • Final report due in July 2011 • Need results to be applied to 2006-2010 ACS for the 5-year CTPP (delivery in summer 2012) • Westat, Tom Krenzke, PI

  11. NCHRP 08-79 (1) Task 1: Review several approaches, including deterministic as well as random error applied to microdata records. Task 2: Select 3 microdata approaches to test, and separated the CTPP tables into 2 sets: A: those without DRB thresholds, and B: those with DRB thresholds

  12. NCHRP 08-79 (2) • Task 3: Develop and evaluate the 3 approaches to mask the underlying microdata • 4 test sites: Atlanta, Iowa, Madison, St. Louis • 2 amounts: Full, Partial replacement • Task 4: Develop data utility and disclosure risk measures • Compare perturbed and “true” ACS with travel model outputs • Discussions with CB’s Disclosure Review Board

  13. NCHRP 08-79 (3)What is a credible method? • Must be implementable at the CB • Schedule: Validate best approach Jan 2011. • Must pass the DRB approval • SAS code which can be modified by CB ACSO staff • Computer processing time • Interative processes must converge quickly • Bayesian approaches must not “run forever” • Results must make sense to transportation analysts • Preserve the descriptive qualities • Should not result in erroneous diagnosis for validating home-based work trips in travel demand forecasting models.

  14. Alternatives to ACS (and other household surveys) for transportation planning? • Societal changes in privacy and information access • Survey response rates continue to decline • Response bias: Young, African American, Hispanic, low-income • Look for voluntary approaches (opt-in) • Greater use of administrative records (LEHD OTM)

  15. Alternatives–Digital Footprinting • Smartphones + GPS • Mobile Millenium (UC) • Nokia, AT&T • Bluetooth tracking • RFID, including toll tags

  16. O/D matrices using Bluetooth monitoring 10121 10115 F S S M T W R F S S M

  17. Balancing issues Digital Footprinting Anonymous High currency Highly detailed geog New private sector partners Lose link to demographics ACS Masked (Synthetic) Requires 5 years accumulation Link between demographics and behavior

  18. Thank you for your attention!Opinions are my own and do not necessarily reflect USDOT policies. • Elaine Murakami • FHWA Office of Planning (Wash DC) • 206-220-4460 • Elaine.murakami@dot.gov

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