Using 5-year ACS for Transportation Planning Applications

Elaine MurakamiFHWA Office of Planning

Elaine.murakami@dot.gov206-220-4460 (in Seattle)

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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

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To/from work

Commuting is key factor in congestion

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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 flow4

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.

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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

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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.

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:How many ACS records per tract or TAZ after 5

years of ACS data accumulation?

Census Tract TAZ (assume 5/tract)

Unweighted hhlds

120 24

Unweighted workers

150 30

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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”)

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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

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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

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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

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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.

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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)

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Alternatives–Digital Footprinting

• Smartphones + GPS

• Mobile Millenium (UC)– Nokia, AT&T

• Bluetooth tracking

• RFID, including toll tags

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10111 10112 10113 10114 10115 10116 10117 10118 10119 10120 10121 1012210111 -- 6707 1068 560 120 137 250 187 174 117 143 10710112 6885 -- 1324 747 197 169 175 277 112 120 259 12110113 872 1067 -- 1228 357 176 53 388 29 130 510 9810114 401 531 1138 -- 1154 467 190 1387 99 403 1714 29110115 112 185 420 1626 -- 490 587 255 602 721 3449 26610116 72 95 154 596 397 -- 1599 1849 925 840 316 137510117 86 71 22 147 262 638 -- 165 1140 264 203 32910118 176 220 381 1553 95 1812 296 -- 102 357 127 49510119 93 60 28 212 606 1029 794 142 -- 807 443 74210120 38 54 111 456 623 1086 551 381 685 -- 470 45510121 115 201 524 2109 2764 333 377 159 340 443 -- 23010122 43 51 79 275 329 1526 480 477 706 686 237 --

O/D matrices using Bluetooth monitoring

10121

10115

ValuesRow Labels Sum of 15N21 Sum of 21N15

May7-May 180 2248-May 292 2159-May 289 16410-May 418 31411-May 399 35712-May 400 35013-May 395 34814-May 383 33815-May 273 19316-May 254 17917-May 166 82

Grand Total 3449 2764

F S S M T W R F S S M

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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) – 206-220-4460– Elaine.murakami@dot.gov

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