Using 5-year ACS for Transportation Planning Applications Elaine Murakami FHWA Office of Planning (in Seattle) 1

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 2 To/from work

Commuting is key factor in congestion 3

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

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

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 6

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. 7

: How many ACS records per tract or TAZ after 5 years of ACS data accumulation? Census TractTAZ (assume 5/tract) Unweighted hhlds Unweighted workers RESULT of this number of unweighted records with the DRB rules  LOTS OF SUPPRESSSION

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”) 9

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 ACS for the 5-year CTPP (delivery in summer 2012) Westat, Tom Krenzke, PI 10

NCHRP (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 11

NCHRP (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 12

NCHRP (3) What is a credible method? Must be implementable at the CB Schedule: Validate best approach Jan –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. 13

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) 14

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

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

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

Thank you for your attention! Opinions are my own and do not necessarily reflect USDOT policies. Elaine Murakami –FHWA Office of Planning (Wash DC) –