Transportation leadership you can trust.

presented topresented to

TRB Census Data for Transportation Planning MeetingTRB Census Data for Transportation Planning Meeting

presented bypresented by

Kevin TierneyKevin TierneyCambridge Systematics, Inc.Cambridge Systematics, Inc.

May 12, 2005May 12, 2005

Learning to Use the ACS for Transportation PlanningReport on NCHRP Project 8-48

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National Cooperative Highway Research Program Project 8-48Project Activities

Review current and potential use of census-related data in transportation planning

Compare residence-based, workplace-based and home-to-work outputs from ACS and census long form for use in transportation planning applications

Prepare ACS guidebook

Recommend new transportation data products based on ACS data

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ACS for Transportation PlanningBenefits

Key Census Bureau objectives are likely to be achieved with ACS implementation

• Improve the year 2010 Decennial Census

• Operational schedules and budgets close to predicted levels

ACS data quality is likely to be superior to that of the Census Long Form in terms of nonsampling error

ACS data will be available more frequently

ACS data will be more timely

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ACS for Transportation PlanningChallenges

Sampling error is higher for ACS than for the Long Form (smaller sample sizes)

Data disclosure avoidance will prevent many smaller area analyses that transportation users would like to do, including some that are possible with Census 2000 data

ACS differences from the Census Long Form place limits on our ability to bridge analyses between Year 2000 data and ACS data

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Data Quality ImprovementACS Three Year Averages versus Census 2000 Long Form

CharacteristicCharacteristicACSACS

(1999-2001)(1999-2001) Census 2000Census 2000

Self Completion Non-Response Rate 44.7% 31.9%

Total Housing Unit Non-Response Rate 4.4% 9.7%

Occupied Housing Unit Non-Response Rate 5.2% 8.7%

Allocation Rates

Population Item Total Allocation Rate 6.5% 11.2%

Occupied Housing Unit Total Allocation Rate 7.7% 15.8%

Vacant Housing Unit Total Allocation Rate 23.2% 19.8%

Population and Occupied Housing Unit Total Rate 6.9% 12.8%

Sample Completeness Rates

Housing Sample Completeness 92.9% 90.3%

Household Population Sample Completeness 90.4% 91.1%

Source: Census Bureau, 2004.

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Data TimelinessImproved Transportation Planning Analyses

Analyses of large geographic areas using the most recent Decennial Census data may require the use of data that is 12 to 14 years old

The same analyses using the most recent ACS data can use data that is 8 to 19 months old

Smaller area analyses will require the combination of data from the past several years, but not nearly as far back as the Decennial Census data

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Data FrequencyImproved Transportation Planning Analyses

ACS can better temporally match with other transportation data sources

• Household and on-board surveys

• Transportation ground count data

• Transportation level-of-service data

ACS supports the development of time series trend analyses

• Transportation trend analyses

• Demographic / land-use analyses

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Sample SizeChallenges for Transportation Planning Analyses

Wider confidence intervals

Need for multiyear averaging

Additional threats of sample loss

• Potential future funding limitations

• Voluntary, rather than mandatory participation

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Sample SizeConfidence Levels

Sampling error is higher for ACS than for the Long Form (smaller sample sizes)

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Sample SizeMulti-year Data Averaging

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Sample SizeChallenges of Analyzing Different Multiyear Periods

Percentage of Zero-Vehicle Households by County Subdivision

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Sample SizeChallenges of a voluntary ACS

Making ACS voluntary, rather than mandatory, will result in:

• Significant reduction in the self-completion mail response rate (over 20 %)

• Increase in annual costs by at least $ 59.2 million to maintain reliability

• And/or reduction in the reliability of estimates because of the reduction in the total number of completed interviews

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Disclosure LimitationsChallenges for Transportation Planning Analyses

Disclosure limits will significantly limit small area analyses commonly performed by transportation planners

Example of disclosure effects on Census 2000 vs. ACS for Multnomah County

Data Part 3: Without Thresholds

Part 3: With Thresholds Part 1

Total Records

Total Workers

Total Records

Total Workers

Total Workers

Census 2000 8,228 207,120 2,644 147,080 199,220

ACS 6,368 181,563 1,673 118,234 202,024

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Comparisons with Census 2000 Demographic Estimates

Estimate CategoryEstimate CategoryACS (1999-2001) – ACS (1999-2001) –

Census 2000Census 2000

Sex Small

Age Moderate

Race Large*

Hispanic Origin Large

Relationship Large

Tenure Moderate

Household by Type Large

Housing Occupancy Large

Source: Census Bureau, 2004.

* Large is defined as nine or more of 36 test counties; small as fewer than four counties.

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Comparisons with Census 2000 Social Estimates

Estimate CategoryEstimate CategoryACS (1999-2001) – ACS (1999-2001) –

Census 2000Census 2000

School Enrollment Moderate

Educational Attainment Moderate

Marital Status Moderate

Grandparents as Caregivers Small

Disability Large*

Nativity and Place of Birth Moderate

Region of Birth/Foreign Born Small

Language Spoken at Home Large

Ancestry Large

Source: Census Bureau, 2004.

* Large is defined as nine or more of 36 test counties; small as fewer than four counties.

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Comparisons with Census 2000 Housing Estimates

Estimate CategoryEstimate CategoryACS (1999-2001) – ACS (1999-2001) –

Census 2000Census 2000

Units in StructureUnits in Structure Large*Large*

Year Structure BuiltYear Structure Built LargeLarge

Number of RoomsNumber of Rooms LargeLarge

Year Householder Moved into UnitYear Householder Moved into Unit SmallSmall

Number of VehiclesNumber of Vehicles ModerateModerate

House Heating FuelHouse Heating Fuel ModerateModerate

Occupants per RoomOccupants per Room LargeLarge

Housing ValueHousing Value ModerateModerate

Mortgage Status and Mortgage Status and Selected Owner CostsSelected Owner Costs SmallSmall

Source: Census Bureau, 2004.

* Large is defined as nine or more of 36 test counties; small as fewer than four counties.

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Comparisons with Census 2000 Economic Estimates

Estimate CategoryEstimate CategoryACS (1999-2001) – ACS (1999-2001) –

Census 2000Census 2000

Employment Status Large*

Commuting to Work Moderate

Occupation Small

Industry Small

Class of Worker Moderate

Household Income Moderate

Income by Type Large

Family Income Small

Poverty Status Small

Source: Census Bureau, 2004.

* Large is defined as nine or more of 36 test counties; small as fewer than four counties.

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Comparisons with Census 2000 Questionnaire and Data Collection Differences

Questionnaire and data collection implementation differences

• Residency definition

• Reference dates

• Minor wording changes

Questionnaire changes over time will further hinder comparison to Decennial Census and previous ACS data

Geographic definition differences

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Comparisons with Census 2000 Questionnaire Resident Definition Differences

Residency definitions are different between Long Form and ACS

• Long Form: usual residence concept− One place where the person spends most of the time

• ACS: current residence concept and the “two month” rule− Recognizes that people can live in more than one place over

the course of a year

− Suits the ACS because of continuous data collection

− Is especially important in seasonal areas

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Comparisons with Census 2000 Questionnaire Reference Period Differences

Reference time periods are different between Long Form and ACS

• Long Form: reference period for a characteristic is a point in time April 1 of the Decennial year

• ACS: reference period for a characteristic is: − An average over 12 months for annual estimates

− An average over 3 years for a 3-year moving average estimate

− An average over 5 years for a 5-year moving average estimate

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Comparisons with Census 2000 Questionnaire Wording Differences

The wording of some questions is different between Long Form and ACS

• Wording and order of introductory data items− ACS collects detailed information on 5 household members

− Long Form collects detailed information on 6 household members

• Wording differences in the instructions for the housing questions

• Effect on trend analysis when there are wording changes

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Comparisons with Census 2000 Geographic Definition Differences

ACS annual and multi-year estimates summarized by the geographic definitions of the final year of the estimates

Definitional changes and annexations need to be accounted for

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Guidebook ACS User Concerns

Census Data Analyses

• Descriptive Analyses

• Trend Analyses

• Transportation Market Analyses

• Travel Survey Development and Analyses

• Travel Demand Modeling Analyses

User Concerns

• Data Frequency Improvements

• Data Timeliness Improvements

• Sample Size Limitations

• Multiyear Averaging Issues

• Data Disclosure Issues

• Bridging between Census 2000 and ACS

• Data Presentation

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Considerations in Defining Transportation Data Products and Special Tabulations

Data needs vary by transportation users

Considerably more transportation planning data may be available from standard ACS tabulations than from standard Decennial Census products

Census Bureau and FHWA have raised concerns about how analysts will treat overlapping multiyear averages

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Considerations in Defining Transportation Data Products and Special Tabulations

Availability of flow data special tabulations with acceptable suppression is in question

Ability to define customized geographic areas for tabulations will be limited

Opportunity to average more than five years of data to increase sample sizes, but the number of years that can be pooled together will reach a practical limit especially in fast growing areas