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APPENDIX D THE DECENNIAL CENSUS AS A SOURCE OF
DATA FOR THE ANALYSIS OF ENVIRONMENTAL JUSTICE
A recent NCHRP research project includes a detailed discussion of census data products and
their usefulness as a source of data for the analysis of environmental justice (Cambridge
Systematices, Inc. 2002). The contents of this appendix was borrowed from that research project.
INTRODUCTION
The Census of Population and Housing (decennial census) is one of the most important sources
of demographic and socioeconomic data to support an analysis of environmental justice.1 Once a
decade, during the first week in April, personnel from the Census Bureau count all the housing
units and people across the United States. The information collected from the census is
disseminated in a variety of ways depending on purpose, geographic unit of reporting, the
questionnaire used to collect the information (short form or long form), avoidance of individual
disclosure, and end-user requirements.
Because of the scope of the census, the wide area of coverage, and large sample size, the
decennial census is a very important source of demographic data that can advantageously be used
to identify emerging transportation planning concerns, especially those related to environmental
justice. This appendix addresses products of the year 2000 decennial census and their application
to the analysis of environmental justice.
The appendix is divided into three sections. To use the information collected from the census, the
user needs to understand basic census concepts. Accordingly, the first section defines data
collection approaches, units of geography, data concepts, availability, and mapping issues. The
section is designed to provide an introductory tour of the census, along with notes on how and
what data to use for analysis of environmental justice. The second section provides detailed
information on some key Census Bureau reporting products. The final section then provides an
introductory exploration of data sources other than the decennial census that can provide
supplemental information.
CENSUS CONCEPTS
This section provides an overview of census concepts relative to environmental justice
analysis. To use the information from the census effectively, the user needs to determine the
following:
1) Are the data (or package) based on data from the short form or the long form?
2) What is the geographic detail at which the data are reported?
1
The information contained in this appendix is based on material contained on various Census Bureau
Web sites.
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3) When will the data be available?
4) How can these data be supplemented with other sources of data?
Short form versus long form data
Five out of six people across the country receive the census short form. This form contains basic
information on individuals and housing. For example, the 2000 short form included only seven
subjects: name, sex, age, relationship, ethnic origin, race, and housing tenure (whether home is
owned or rented). One out of six people (17 percent of households) receive the census long form.
This questionnaire includes 52 questions covering topics such as educational level, income,
ancestry, housing conditions, commuting patterns, disability, veteran status, and employment.
In general, if the desire is to look for complete counts of all people or housing units at the block
level, the smallest unit of census geography, releases that are packaged from the short form
should be used. Examples where information from the short form may be needed include
neighborhood-planning analysis to find relative distributions of minority population groups or to
find relative population distributions in a rural location. Important releases that use short form
data include the Census Bureau redistricting file (PL-94-171 file) and the Summary Files 1, 2,
and 4 (SF 1, SF 2, and SF 4).
At a somewhat higher geographic level (block groups and census tracts), information from the
long form can be used. For example, if the desire is to investigate specific travel-related issues or
ascertain telephone availability by race to conduct a telephone survey, only the Census Bureau
released long form data can be used. The important packages containing long form data include
Summary File 3 (SF 3) and the Census Transportation Planning Package (CTPP).
Geographic detail
The Census Bureau uses a hierarchy of "geography" to report data. Key geography delineations
include (in the increasing order of size) census blocks, census block groups, census tracts, traffic
analysis zones (comparable in size to block groups in urban areas and tracts in rural areas),
voting districts, places, counties, states, and the nation.
Census blocks are the smallest area of census geography, normally bounded by streets or other
prominent features. They may be as small as a city block bounded by four streets or as large as
100 square miles in rural areas. Blocks are basic units and building blocks of the Census Bureau
geographic hierarchy. Blocks are used to report only selected population counts obtained from
the census short form.
Block groups consist of a set of census blocks identified by the same census first digit as the
next higher hierarchy, the tract.
Census tracts are areas containing, on average, roughly 4,000 people. Counties and equivalent
areas are subdivided into census tracts. Most of the information collected from the long form is
reported at the block-group or tract level.
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Traffic analysis zones (TAZs) are a new unit of geography in the 2000 census. They are
included as part of the Census Transportation Planning Package. TAZs have been defined
collaboratively by metropolitan planning organizations (MPOs) working with the Census Bureau
through the TAZ-UP program. While TAZs have been defined for over 1,400 counties, not all
areas of the country have defined TAZs as a separate unit of geography for census reporting.
Voting districts are areas such as election districts, wards, or precincts identified by states.
Places are typically cities (in urban areas) or minor civil divisions (such as townships) in
rural areas.
The Census Bureau periodically releases digital files called "TIGER/Line." The TIGER/Line
files are a digital database of geographic features, such as roads, railroads, rivers, lakes, political
boundaries, and census statistical boundaries covering the entire United States. For 2000, the
Census Bureau released a version of TIGER/Line 2000 in early 2001 to accompany the PL-94-
171 redistricting data. This file contains the final TAZ layer for all organizations that participated
in the TAZ-UP program. However, this initial file did not contain zip code tabulation areas
(polygon areas derived from post office zip codes) and did not include the new address ranges
obtained in 2000. A second version of census 2000 TIGER/ Line files containing this updated
information was released in April 2001.
Mapping and GIS overlays
TIGER/Line can be used along with the other census packages to develop complete GIS
databases for every area in the United States. TIGER/Line files are easy to convert to GIS files in
almost all commercially available software.
Most of the key census tables useful for an environmental justice analysis are available at the
tract, block-group, and TAZ level. Each area, therefore, can be examined in a GIS environment.
For example, key household information, such as income, race, presence of elderly population,
vehicle ownership, and physically handicapped status, can be overlaid with travel-related
information (such as travel time) to analyze the benefits and impacts to minority tracts or block
groups.
If an agency has other sources of information, new data layers can easily be brought into the GIS
environment, and overlaid on top of the census information. For example, transit availability can
be mapped over area characteristics obtained from the census and, by using several thematic
maps, a visual inspection of population groups benefiting from transit can be obtained. More
complex analyses, such as creating buffers and examining corridor characteristics can also be
performed with standard GIS software packages. A significant advantage of using census data is
that they allow for precise spatial analysis at small levels of geographic detail.
Mapping specific area characteristics can be used as a powerful visual communication tool to
convey planning concepts to neighborhood advisory committees, a key requirement for
environmental justice.
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Data availability
When will data be available? The Census Bureau processes short form data first and then the
long form data. Packages containing the short form data are released first, followed by the long
form data. Table D-1, shows the relative dates of release, along with the lowest level of
geography for key packages containing the short and the long form data. Table D-5, located at
the end of this appendix, provides a detailed listing of all standard census products.
Table D-1
Key census 2000 products
Long form data products
Short form data products (Contents = age, income, occupation, mobility,
(Contents = race, basic housing counts) industry, commute, and vehicle ownership)
Lowest level Lowest level
Release date File geography Release date File geography
Data available as Census 2000 Blocks Data available as Summary File 3 Block Groups
of April 2001 Redistricting of September (SF 3)
Data File 2002
(PL-94-171)
Data available Summary File 1 Blocks Data available Census Transportation
as of September (SF 1) as of Spring Transportation analysis zones
2001 2003 Planning Pkg. (TAZ)
Source: U.S. Census Bureau, Population Division, Decennial Programs Coordination Branch.
How to look for specific tables in a census package. The Census Bureau divides tables broadly
into person tables and household tables. Person tables can be defined for all workers, all persons,
and persons over 18 (called a "universe" in the census packages). Once the package and table
type are identified, it is relatively easy to go through the data dictionaries to locate the exact
table. For example, if a planner is looking for a table containing household counts by poverty
status and mode used for work, the likely package would be the Census Transportation Planning
Package (CTPP). The likely table would be a residence end table containing household counts.
What release to use and when? If an agency desires to do some early analysis with basic racial
and ethnicity data, the redistricting file provides this capability. If basic data (one-way, two-way,
or three-way tables) containing detailed income, physically handicapped status, or elderly status
are the variables needed, the Summary File 3 (SF 3) or the CTPP are required. If detailed
journey-to-work flow information or travel-related information by place of work are required,
then the CTPP is the only choice. More detailed information on package content is provided in
the following section.
In addition to the standard tabulations, the Census Bureau also allows users to make custom
tables through the Internet via a portal called the American FactFinder (AFF). Using the AFF,
specific tables can be defined for an area without depending on any standard package.2
2
The Internet site is http://factfinder.Census.gov/
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DECENNIAL CENSUS PRODUCTS
The Census Bureau disseminates information collected from the decennial census through
several packages. Each package, or release, is meant for a specific purpose. For example, the
redistricting file (PL-94-171) is released primarily for the purposes of election redistricting, and
it is required by law that the Census Bureau should release 100 percent counts of the population
within 1 year following the date of collection. In 1990, there were five packages that contained
information at lower levels of geography:3
· PL-94-171 Redistricting data,
· Summary Tape File 1,
· Summary Sample Tape File 3,
· Subject Summary Tape Files, and
· Census Transportation Planning Package (CTPP).
PL-94-171 Redistricting data. Congress passed Public Law (PL) 94-171 in 1975, offering states
the opportunity to receive population totals for election precincts and similar areas. From 1990
onwards, states have been receiving population data by race at the block level to support
redistricting. The PL-94-171 file is based on a 100 percent sample (the census short form) and
contains the most detailed information on the location of the total population by race and ethnic
origin and on population over the age of 18 (voting population) by race and ethnic origin.4
The PL-94-171 file is important because it is one of the first products released after the decennial
census. The data for 2000 were released by April 2001 and accompanied by software to access
the data. The file contains various tabulations:
1) Six "single race" tabulations, namely African Americans, American Indian/Alaska
Native, Native Hawaiian and other Pacific Islander, Asian, White, and some other race.
2) Fifty-seven combinations for those that marked "more than one" of the six race
categories.
Implications of "more than one race." Environmental justice requires "all impacted minority
groups" to be identified as a first step in the analysis. A memorandum issued by the Office of
Management and Budget (OMB Bulletin No. 00-02) requires that for those that marked more
3
Summary File 2 and 4 also represent major census reporting packages. Summary File 2 (SF 2) contains 47 detailed
tables focusing on age, sex, households, families, and occupied housing units for the total population. These tables
are repeated for 249 detailed population groups. Summary File 4 (SF 4) contains population and housing
characteristics iterated for many detailed race and Hispanic or Latino categories, American Indian and Alaska
Native tribes, and ancestry groups. While SF 2 and SF 4 contain more detailed race and ancestry information, the
higher-level reporting contained in SF 1 and SF 3 is expected to be sufficient for most analyses of environmental
justice.
4
Agencies can get a copy of the software and the data via the Internet or their local state data center contact. For
more information on the redistricting program, visit the Census Bureau Web site at http://www.Census.gov/clo/
www/redistricting.html. Instructions for transferring the redistricting data to a GIS are provided at
http://www.fhwa.dot.gov/planning/census/pl2gis.htm.
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than one race, if one of the categories is a minority category, then that person should be included
as a minority. For people that marked more than two races, the most adversely impacted
community among the three should be treated as their race. However, analyses conducted by the
Census Bureau show the numbers of people that marked more than two races to be a very small
proportion of the total population.
For those organizations that defined TAZs for TIGER 2000, a TAZ field is included in the
redistricting file so that users can aggregate blocks into TAZ summaries. This is an improvement
over the 1990 package because it allows locally developed TAZ-level information to be easily
overlaid with the PL-94-171 data.
The PL-94-171 data constitute an important source of information that can be immediately used
in transportation planning to support an environmental justice analysis. Although the Census
Bureau provides far less data at lower geography levels (such as block groups), the PL-94-171
file contains extensive data on race and ethnicity. The data can be used to analyze the
concentrations of minority population groups. Since the data are released at the block level,
precise spatial disaggregation can be performed, which in turn can help with analyzing the
impacts of transportation related projects on different groups.
Strengths of PL-94-171 file. There are three main strengths:
1) It is the first file released (April 1, 2001, is the legal deadline for the Census Bureau).
2) A great amount of geographic detail is retained.
3) It contains the greatest detail on race and ethnic origin.
Weaknesses of PL-94-171 file. The file does not contain information on households or other
characteristics such as income, physical mobility status, and age, which are desirable in fully
defining minority groups for environmental justice purposes.
Summary File 1 (Summary Tape File 1 in 1990)
The Summary File 1 (SF 1) contains data from the short form and includes population counts by
age, race, sex, marital status, ethnic origin, household type, and household relationship.5 In the
1990 file, population items were cross-tabulated by age, race, ethnic origin, or sex. Housing
items included occupancy/vacancy status, tenure, units in structure, contract rent, meals included
in rent, value, and number of rooms in housing unit. For 2000, the state-by-state release of SF 1
was completed by the Census Bureau between June and September 2001.
SF 1 contains the 100 percent data, which is the information compiled from the questions asked
of all people and about every housing unit. Population items reported include sex, age, race,
5
The FHWA portal on census issues contains information on SF 1 data. Procedures to convert the data to a GIS and
to aggregate the block data to traffic analysis zones are also provided. For further information see
http://www.fhwa.dot.gov/planning/Census/sf1.htm.
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ethnicity, household relationship, and group quarters. Housing items include occupancy status,
vacancy status, and tenure (owner occupied or renter occupied).
There are 171 population tables (identified with a "P") and 56 housing tables (identified with an
"H") available at the geographic detail of census blocks. In addition there are 59 population
tables with detailed race and ethnic origin available at the geographic detail of census tracts
(identified with a "PCT") for a total of 286 data tables. For major race and Hispanic or Latino
groups, there are 14 population tables and 4 housing tables shown down to the block level and 4
population tables shown down to the census-tract level.
Strengths of SF 1. The three primary strengths are as follows:
1) The data are released between June and September 2001, a year earlier than long-form
data.
2) The data contain at least basic information on housing units as opposed to the PL-94-171
file.
3) The data are available at the block level.
Weaknesses of SF 1. Important information for environmental justice such as income,
physically handicapped status, and commute characteristics (essentially long-form
characteristics) are not available.
Sample Summary File 3 (Summary Tape File 3 in 1990)
The Summary File 3 (SF 3) contains long-form sample data weighted to represent the total
population. In addition, the file contains 100 percent counts and unweighted sample
counts for total persons and total housing units. Most of the tabulations in the 1990 STF3
were two-way tables. For example, some of the race tabulations in the 1990 STF3 included the
following:
· Table P86. Age of householder (7 categories) by household income in 1989 (9
categories) Universe: Households.
· Table P87A. Race of householder (1 category) by age of householder (7 categories) by
household income in 1989(9 categories) Universe: White households.
· Table P87B. Race of householder (1 category) by age of householder (7 categories) by
household income in 1989(9 categories) Universe: Black households.
· Table P87C. Race of householder (1 category) by age of householder (7 categories) by
household income in 1989(9 categories) Universe: American Indian, Eskimo, or Aleut
households.
· Table P87D. Race of householder (1 category) by age of householder (7 categories) by
household income in 1989(9 categories) Universe: Asian and Pacific Islander
household.
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· Table P87E. Race of householder (1 category) by age of householder (7 categories) by
household income in 1989(9 categories) Universe: Other race households.
· Table P88. Age of householder (7 categories) by household income in 1989 (9
categories) Universe: Households with householder of ethnic origin.
Population items covered by the 1990 STF3 relevant to environmental justice analysis include
age, mobility limitation status, ancestry, occupation, citizenship, place of birth, class of worker,
place of work, educational attainment, poverty status, ethnic origin, sex, household type and
relations, travel time to work, income in 1989, urban and rural population, industry,
veteran/military status, language spoken at home, work disability status, marital status, work
status in 1989, means of transportation to work, and workers in the family in 1989.
Relevant housing items in the 1990 STF3 include age of householder, race of householder, ethnic
origin of householder, telephone availability, vehicles available, selected monthly owner costs,
condominium status, tenure, units in structure, housing units, value of housing unit, mortgage
status, occupancy status, and rent.
A draft of the SF 3 specifications for 2000 are available at the Census Bureau State Data Center
(SDC) Web site (http://www.sdcbidc.iupui.edu/Census_2000/census_2000.html). SF 3 is
expected to be released from June to September of 2002. The residence information for the
Census Transportation Planning Package is being released in 2004. This package contains most
of the important long form information useful for transportation planning applications.
Strengths of SF 3. There are three main strengths:
1) The SF 3 contains additional information to support an analysis of environmental justice.
2) Cross tabulations such as race and income can help in developing more complete
definitions of environmental justice populations.
3) In association with SF 1, the SF 3 package can be used to effectively support all types of
microarea analysis.
Weaknesses of SF 3. The three principal weaknesses are as follows:
1) The data are released 2 years after collection.
2) The lowest level of geographic detail is at the block group. This is inherently true of
all packages derived from the sample, or long-form, questionnaire.
3) The SF 3 contains few three-way tabulations.
Subject summary tape files
Additional subject summary tabulations (SSTF) were provided by the Census Bureau in 1990.
For the 2000 Census, the user will be allowed to make custom tables by using the American Fact
Finder portal. The 1990 tabulations of interest include the following:
· The foreign-born population in the United States (SSTF01);
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· Persons of ethnic origin in the United States (SSTF03);
· Characteristics of adults with work disabilities, mobility limitations, or self-care
limitations (SSTF04);
· The Asian and Pacific Islander population in the United States (SSTF05);
· Education in the United States (SSTF06) and employment status, work experience, and
veteran status (SSTF12);
· Metropolitan housing characteristics (SSTF07);
· Housing of the elderly (SSTF08);
· Housing characteristics of new units (SSTF09);
· Mobile homes (SSTF10);
· Employment status, work experience, and veteran status (SSTF12);
· Characteristics of American Indians by tribe and language (SSTF13);
· Occupation by industry: 1990 (SSTF14);
· Geographic mobility in the United States (SSTF15);
· Poverty areas in the United States (SSTF17);
· The older population of the United States (SSTF19);
· Journey to work (SSTF20);
· Characteristics of the black population (SSTF21); and
· Earnings by occupation and education (SSTF22).
Census Transportation Planning Package
The CTPP is a set of special tabulations derived from the decennial census designed specifically
for transportation planning. CTPP contains tabulations by place of residence (Part 1), by place of
work (Part 2), and for flows between home and work (Part 3). The level of aggregation used is
the TAZ for those counties that have a TAZ layer defined in TIGER/Line. For other metropolitan
areas, the lowest level of geography is the tract or block group, depending on the choice of the
local MPO. The CTPP is part of the third tier of data products released by the Census Bureau.
The 1990 CTPP contained several tabulations useful for an environmental justice analysis.
Tables D-2 and D-3 are extracts from the data dictionary of the 1990 CTPP.
The CTPP 2000 standard tabulations contain roughly 30 tables useful for an environmental
justice analysis. A significant addition is the introduction of a flow table in Part 3 consisting of
minority population flows by origin and destination. Another important feature of the CTPP is
that it contains tabulations both by work and home end. Moreover, the tabulations at the work
end are "mirrored" by tabulations at the home end. "Mirrored" tables enable CTPP users to
estimate the flow of workers from their place of residence to their place of work by household
and worker characteristics. With techniques such as the Fratar method (a method for applying
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growth factors to traffic within origin-destination tables) or iterative proportional fitting (IPF),
users can estimate worker flow tables that will not be included in the CTPP 2000 standard
tabulations.
Table D-2
Residence end (Part 1)
Table Tabulation
1-5 Universe: Persons; Ethnic Origin (3 categories) by Race (4 categories)
1-9 Mobility limitation status (3 categories) by age (11 categories)
Universe: Persons 16 years and over
1-10 Mobility limitation status (3 categories) by employment status (6
categories)
Universe: Persons 16 years and over
1-24 Ethnic origin (3 categories) by race (4 categories) by means of
transportation to work (11 categories).
Universe: Workers 16 years and over
1-44 Mobility limitation status (3 categories) by means of transportation to work
(11 categories)
Universe: Workers 16 years and over
Table D-3.
Work end (Part 2)
Table Tabulation
2-1 Ethnic origin (3 categories) by race (4 categories) by means of transportation to
work (11 categories)
Universe: Workers 16 years and over
The CTPP, combined with SF 3 and SF 1, is a powerful tool to develop significant data
capabilities needed for an environmental justice analysis. Worker flows between residence and
workplace and the workers' household characteristics and travel behavior are reported in the 10
tables in this group and provide information on household income, vehicle availability, and mode
of travel to work. The CTPP also contains many tables (at both the residence and the work end)
with poverty, elderly, and disability status; and race and ethnic origin combined with income. In
addition, there are many three-way tables specifically designed with the analysis of
environmental justice as an objective. A few small four-way tables also are included.
The cross-tabulations of race by income, race by occupation, and race by industry are very
powerful tools to derive indices and develop estimates of most significantly impacted population
groups. These cross-tabulations, in turn, can assist in classifying households based on
characteristics such as poverty tracts or delineating areas needing transit access. For example,
geographic areas dependent on transit can be defined using a table in CTPP with household
counts of the following four cross-tabulated characteristics:
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· Poverty status (income less than 100 percent, between 100 and 150 percent, or greater
than 150 percent of poverty threshold);6
· Race (white, black, other);
· Ethnic origin; and
· Mode (single-occupancy vehicle, carpool, transit, etc.).
Strengths of the CTPP. There are five primary strengths:
1) Tabulations at the work end are provided.
2) Minority status population group worker flows are tabulated by origin and destination.
3) Along with SF 1 and SF 3, CTPP completes the information that can be derived from the
census standard products.
4) The new CTPP design specifically considers environmental justice analysis requirements.
5) The CTPP can be used for tract-level, place-level, county-level, or even for statewide
analyses.
Weakness of the CTPP. The most important weakness is the following:
1) The tabulations contain fewer categories (e.g., race is divided into only four categories
for Parts 1 and 2). This was done to increase the number of cross-tabulated variables. The
package needs to be used in conjunction with SF 1 and SF 3 to draw the maximum
benefits. For the Part 3 origin and destination flow reporting, all minority population
groups are combined into a single category because of the potentially small sample
sizes associated with many of the individual cells.
Other sources of demographic data
Although the decennial census is the most important source of information for reliable
data on race, ethnicity, income, age, and physically handicapped status, it only provides a
snapshot in time. To obtain data on a noncensus year, it is necessary to rely on a
combination of estimation techniques based on the use of census data and information
from other survey and data sources. This subsection provides an introduction to five
potential supplementary data sources:
· American Community Survey,
· American Housing Survey,
· Current Population Survey,
· Nationwide Personal Transportation Survey, and
6
A listing of poverty tracts is contained at the Census Bureau Web site, http://www.census.gov/hhes/www/
poverty.html
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· Other commercial sources.
American Community Survey
The American Community Survey (ACS) is a continuous survey performed by the Census
Bureau. The ACS data constitute a paradigm shift from a "snapshot" approach to one of
continuous collection across time.7 When implemented fully, it will provide information on
demographic, economic, and housing profiles of America's communities every year. The ACS
has the same questionnaire content as the decennial long form and is expected to replace the long
form in 2010. Between 1999 and 2001, the ACS was conducted in 31 sites to compare ACS
results with those from the census 2000 long form. Full implementation of the ACS is planned to
begin in 2003 for every county in the country and will achieve the same one-in-six sample size
as the census long form.
Table D-4 lists data availability for different areas. The ACS data from the test sites are available
as of the middle of July 2001. The earliest data from the fully implemented ACS are expected to
be available in 2004 for areas having a population greater than 65,000.
Table D-4
Availability of American Community Survey data
Expected release
Area characteristics date of ACS data What will be released
Population greater than or equal to 65,000 2004 Yearly data
Population between 20,000 and 65,000 2006 Three-year average
Population below 20,000 (e.g., census tracts or 2008 Five-year average
block groups)
The Bureau of Transportation Statistics (BTS) has produced a report entitled Implications of
Continuous Measurement for the Uses of Census Data in Transportation Planning (BTS 1996).8
This report presents the findings of an expert panel on the utility of data obtained from
continuous measurement for transportation planning. The report found that a change from the
traditional long form to continuous measurement can significantly affect how state and
metropolitan transportation planners use decennial census data. The continuous measurement
process, however, is a new process, and the results need to be compared and evaluated against
those from the conventional census.
7
Additional information on the American Community Survey is available at the Census Bureau
Web site, http://www.Census.gov/acs/www.
8
A copy of this report and a discussion on the American Community Survey from a transportation perspective can
be accessed at http://www.trbcensus.com/acs/.
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American Housing Survey
The American Housing Survey (AHS) collects data on the nation's housing.9 The AHS consists
of a national sample of 55,000 households, collected every year. The AHS also samples 47
selected metropolitan areas once every 4 years. The sample size for each area is 4,800
households. Though the AHS is primarily designed to collect data on the nation's housing stock,
the survey also contains several questions relating to race, income, household size, vehicle
ownership, and journey to work. The survey is conducted by the Census Bureau for the U.S.
Department of Housing and Urban Development (HUD). The AHS returns to the same housing
units each time to gather data. While the sample size for the AHS is relatively small, the data can
be used to develop inter-censal estimates at a county level. Moreover, data from two or three
surveys can be combined and weighted with population estimates to obtain estimates at a tract
level.
Current Population Survey
The Current Population Survey (CPS) is a joint venture of the Census Bureau and the Bureau of
Labor Statistics (BLS). The survey has been conducted for more than 50 years. The sample size
for the survey is expected to increase to 99,000 households nationwide in the near future.10 The
sample is scientifically selected to represent the civilian noninstitutional population.
Respondents are interviewed to obtain information about the employment status of each member
of the household 15 years of age and older. Published data, however, focus on those ages 16 and
over. Although the CPS is designed primarily to collect up-to-date information for states, it can
be used in conjunction with other census-related products to develop estimates at lower level
geographies.
Estimates obtained from the CPS include employment, unemployment, earnings, hours of work,
and other indicators. These are available by a variety of demographic characteristics including
age, sex, race, marital status, and educational attainment. They also are available by occupation,
industry, and class of worker. Supplemental questions often are added to the regular CPS
questionnaire to produce estimates on a variety of topics including school enrollment, income,
previous work experience, health, employee benefits, and work schedules.
Because the sample size for both the CPS and AHS are very small, the data from these surveys
need to be combined and weighted with the decennial census data to obtain estimates of various
characteristics not collected in the decennial census. Several methods can be used to weight the
census data. Methods commonly used to iterate the data include IPF and Bayesian techniques.
9
The Census Bureau Web site provides comprehensive information on the American Housing Survey at
http://www.Census.gov/hhes/www/ahs.html.
10
More information on the Current Population Survey is available at http://www.bls.Census.gov/cps/cpsmain.htm.
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Nationwide Personal Transportation Survey
The Nationwide Personal Transportation Survey (NPTS), now renamed as the National
Household Transportation Survey (NHTS), provides a periodic snapshot of daily travel from a
sample of 25,000 U.S. households. The data provided by the NHTS cover all trips made by all
household members, by all modes and trip purposes, in a single travel day. First collected in
1969, subsequent rounds of data were collected in 1977, 1983, 1990, and 1995. A new round of
NHTS data collection became available in 2003.
The survey includes questions similar to those in the decennial census about the respondent's
"usual" journey to work. This permits comparison of how people interpret the question about
their "usual" mode to work with how they actually travel to work on a specific survey day. A
few organizations and states purchase add-on samples of the NHTS to use in place of a local
household travel survey for regional travel forecasting purposes. Because the NHTS contains
information on nonwork modes, the data can be weighted with the CTPP data and used to
analyze all types of travel characteristics of all special population groups. A summary of relevant
census products and approximate release dates are presented in Table D-5.
Other commercial sources
Data from the decennial census provides information for a specific day once every 10 years.
More current data, however, are often desirable for an environmental justice analysis. Several
other Census Bureau surveys and other federal government surveys can be combined to produce
updated estimates at small areas of geography, as indicated in the previous subsections. The ACS
is expected to be particularly helpful in this regard when it becomes fully operational. In
addition, Claritas Corporation continuously updates the census data at the block-group level and
releases an updated dataset every year.
Table D-5.
Timeline for standard census products
Release date 100-percent data products Lowest level Media
March 2001 Census 2000 Redistricting Data Summary File Census blocks Internet
State population counts for race and Hispanic or CD-ROM
Latino DVD
May-June 2001 Demographic Profile Places Internet
Selected population and housing characteristics in a CD-ROM/DVD
single table. Paper
May 2001 Census 2000 housing unit counts Places Internet
May-June 2001 Congressional District Demographic Profile Congressional Internet
Same as the demographic profile but for districts of the CD-ROM/DVD
Congressional districts 106th Congress Paper
June 2001 Race and Hispanic or Latino Summary File Places Internet (FTP)
CD-ROM
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Table D-5.
Timeline for standard census products (continued)
Release date 100-percent data products Lowest level Media
States: Summary File 1 (SF 1) Census blocks Internet
June-Sept. 2001 Population counts for 63 race categories and Census tracts CD-ROM
Hispanic or Latino Census blocks/ DVD
Advanced national: Population counts for many detailed race and census tracts
Nov.-Dec. 2001 Hispanic or Latino categories and American
Indian and Alaska Native tribes
Final national: Selected population and housing characteristics
May-June 2002
States: Summary File 2 (SF 2) Census tracts Internet
Sept.-Dec. 2001 Population and housing characteristics iterated for CD-ROM
many detailed race and Hispanic or Latino categories DVD
Advanced national: and American Indian and Alaska Native tribes
Mar.-Apr. 2002
Final national:
June-July 2002
States: Quick Tables Census tracts Internet
Mar.-Dec. 2001 Table shells with population and housing CD-ROM/DVD
characteristics where the user can specify a
National: geographic area and a population group
Nov. 2001-Apr.
2002
States: Geographic Comparison Tables Places Internet
Mar. 2001-Jan. 2002 Population and housing characteristics for a list of CD-ROM/DVD
geographic areas (e.g., all counties in a state)
National:
Nov. 2001-Aug.
2002
Apr. 2002 Advanced Query Function User defined Internet
User specifies contents of tabulations from full down to census
microdata file block groups
Includes safeguards against disclosure of
identifying information about individuals and
housing units
Jan.-Nov. 2002 Summary Population and Housing Places Internet
Characteristics (PHC-1) Paper
2003 Population and Housing Unit Totals (PHC-3) Places Internet
Paper
Mar.-May 2002 Demographic Profile Places Internet
Demographic, social, economic, and housing CD-ROM/DVD
characteristics presented in three separate tables Paper
Mar.-May 2002 Congressional District Demographic Profile Congressional Internet
Demographic, social, economic, and housing districts of the CD-ROM/DVD
characteristics presented in three separate tables for 106th Congress Paper
Congressional districts only
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Table D-5.
Timeline for standard census products (continued)
Release date 100-percent data products Lowest level Media
June-Sept. 2002 Summary File 3 (SF 3) Census tracts Internet
Population counts for ancestry groups Block groups/ CD-ROM
Census tracts DVD
Selected population and housing characteristics
Oct. 2002-Feb. 2003 Summary File 4 (SF 4) Census tracts Internet
Population and housing characteristics iterated for CD-ROM
many detailed race and Hispanic or Latino DVD
categories, American Indian and Alaska Native
tribes, and ancestry groups
June 2002-Feb. 2003 Quick Tables Census tracts Internet
Table shells with population and housing CD-ROM/DVD
characteristics where the user can specify a
geographic area and a population group
July 2002-Mar.2003 Geographic Comparison Tables Places Internet
Population and housing characteristics for a list of CD-ROM/DVD
geographic areas (e.g., all counties in a state)
For 1-percent Public Use Microdata Sample (PUMS) file Super public use CD-ROM
sample: 1-percent sample (information for the nation and microdata areas DVD
2002 states, as well as substate areas where (PUMAs) of
appropriate) 4,000,000+
5-percent sample (information for state and PUMAs of
substate areas) 1,000,000+
Oct. 2002 Advanced Query Function User defined Internet
User specifies contents of tabulations from full down to census
microdata file tracts
Includes safeguards against disclosure of
identifying information about individuals and
housing units
2003 Summary Social, Economic, and Housing Places Internet
Characteristics (PHC-2) Paper
2003 Congressional District Data Summary File Census tracts Internet
100-percent and sample data for the redistricted 108th within CD-ROM
Congress Congressional DVD
districts
Source: U.S. Census. Population Division, Decennial Programs Coordination Branch, July 13, 2001.
REFERENCES
Cambridge Systematics, Inc. 2002. Technical Methods to Support Analysis of Environmental
Justice Issues. Final report of project NCHRP Project 8-36(11). Transportation Research
Board, National Research Council. Washington, DC: National Academy Press.
Bureau of Transportation Statistics (BTS). 1996. Implications of Continuous Measurement for
the Uses of Census Data in Transportation Planning. Washington, DC: U.S. Department of
Transportation.
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