Traffic Analysis Zone (TAZ) Program

January 2011

U.S. Department of Transportation
Federal Highway Administration
Bureau of Transportation Statistics
Federal Transit Administration
AASHTO Standing Committee on Planning
In cooperation with the TRB Census Subcommittee

TAZ Delineation for Use in CTPP

2006-2008 CTPP Released!

Census Bureau Geography Division staff,
geo.taz.list@census.gov
Liang Long, Cambridge Systematics, Inc.
Liang.long@dot.gov

2006-2008 CTPP based on ACS data has
been fully released! Tabulation is limited
to areas with 20,000 residential population
or more. The data with the access software
are available at www.ctpp.aashto.org. Go
check it out! The initial version was
released in mid-January, and upgrades and
bug fixes are rolling in on an as-needed
basis.

February through July of 2011 will be critical
months for Traffic Analysis Zone (TAZ) and
Traffic Analysis District (TAD) delineation for
CTPP. If you are an MPO or state DOT and
want the 2006-2010 CTPP to include tabulations
for TAZs and TADs, you need to allow enough
time to delineate these geographic entities and
submit them to the Census Bureau.
For the first time, two different custom geographic zone systems will be allowed. In addition to TAZs, a new geographic area called a
Transportation Analysis District (TAD) will be
defined. TADs will have a minimum population
threshold of 20,000. The concepts behind the
TADs are to have a geographic unit that meets
the Census Bureau’s threshold for three-year
ACS tabulation, 20,000 people per zone, and to
provide high-quality data. Even if a state or
MPO chooses not to define TAZs, they should
consider defining TADs by aggregating 2010
block groups, 2010 Census tracts, or small rural
counties to avoid the “incomplete coverage”
problem currently found in ACS standard tabulations. (Only cities and counties with more
than 20,000 population are covered in ACS
standard tabulations.)
TAZ Delineation Schedule
• December 2010: Final review of the list of
state and MPO individuals who will be the
point of contact for their areas is delivered
by FHWA to the Census Bureau’s
Geography Division. First prototype version
of the TAZ delineation software, called the

This round of CTPP is using web-based
data delivery. Please refer to the article
written by Paul Agnello for more
information about the data access software.
http://www.fhwa.dot.gov/ctpp/sr1008.htm
Master Address File (MAF)/TIGER
Partnership Software (MTPS) TAZ Module,
delivered to Census Bureau.
•

January 2011: MTPS TAZ Module demonstrations at Transportation Research Board
Annual Meeting at the Census Bureau booth
in the exhibit hall.

•

February 2011: MTPS TAZ Module
training, webinars are tentatively scheduled
for Friday, February 25 and Monday,
February 28 coordinated by FHWA.

•

March through early April 2011: Posting of
MTPS TAZ Module, 2010 Census data, and
geographic shapefiles on a secured web site
for state/MPO download. This will occur on
a rolling basis. Each participating agency
will have three months to delineate their
TAZs and TADs and return the files to the
Census Bureau for review and processing.

(continued on page 2)

Page 2

January 2011

TAZ Delineation for Use in CTPP (continued)
•

June through early July 2011: All files must
be returned to Census Bureau’s Geography
Division within three months after the
receipt of the TAZ/TAD delineation software and data.

TAZ Software Example
Note: The figures shown below do not represent
the final version of the MTPS TAZ Module;
those in the final version may look somewhat
different.
The TAZ delineation software is being
developed by Caliper Corporation. The software, referred to as the MTPS TAZ Module, has
a Geographic Information System (GIS) basis,
similar to their Maptitude product and is a standalone package that does not require purchase
and/or a license(s) to run. The MTPS TAZ

Module allows MPOs and state DOTs to delineate TAZ entities (TAZs/TADs) based on 2010
Census tabulation geography (census tracts,
block groups, or blocks). The module will have
the ability to delineate TAZs only; both TAZs
and TADs; or TADs as aggregates of default
TAZs (e.g., 2010 Census tracts or block groups).
It also will give participants the option of
delineating their 2010 TAZs starting from
scratch; using their TAZs from Census 2000;
creating new TAZs starting from the 2010
Census block groups or 2010 Census tracts; or
by importing block equivalency files (i.e.,
loading your own file in which you already have
assigned TAZ codes to 2010 Census blocks)
(Figure 1).

Figure 1. This image shows the TAZ software map display, toolbox, and start (restart)
settings available to the participant.

January 2011
The MTPS TAZ Module will allow the participant to spatially edit geographic data by adding
and removing area, as well as creating new and

Page 3
deleting existing TAZ entities. The residential
and worker tallies will be updated with each edit
that is made to the TAZ entity (Figure 2).

Figure 2. The grey area represents the TAZ selected for editing. The population and
worker tallies (red circle) change as blocks are added to or removed from the
TAZ.

The MTPS TAZ module contains automated
checks for nesting and overlap issues. For
example, TAZs must nest within counties and
TADs; and TADs must nest within the MPO
(TADs can cross county boundaries). A variety
of participant run checks will help verify that the
delineation has adhered to contiguity, compactness, and minimum population/worker count

requirements. The module also verifies that
there are no unassigned areas and all assigned
codes are unique (Figure 3). Once the MPO or
state DOT has completed their work, the module
will create a ZIP output file, including new
shapefiles and block equivalency files to return
to the Census Bureau’s Geography Division.

Page 4

January 2011

Figure 3. One of the verification checks (unassigned areas) that the MPO or State DOT
must run to verify the delineation of the TAZ/TADs.

The Census Bureau’s Geography Division will
have a booth at the TRB Annual Meeting where
there will be a demonstration of the preliminary
MTPS TAZ Module.
TAZ Software Training
The FHWA, in coordination with the Census
Bureau’s Geography Division, will host two
web-based TAZ software training sessions
(webinars), tentatively scheduled for
February 25 and February 28, 2011. The webinars will demonstrate how to use the MTPS
TAZ module. The webinar will be recorded and
archived on the AASHTO CTPP webinar page.
http://ctpp.transportation.org/Pages/
webinardirectory.aspx

TAZ Delineation Criteria
Agencies are not required to delineate TAZs or
TADs for the CTPP. If an agency chooses not to
delineate TAZs for a county, the 2010 Census
tracts also will become the TAZs for that county.
Even if agencies do not plan to delineate TAZs,
they may want to define TADs by aggregating
block groups, census tracts, or counties together.
The TAZ business rules are posted at the FHWA
webpage: http://www.fhwa.dot.gov/ctpp/
tazddbrules.htm

Census Transportation Planning Products (CTPP) AASHTO Update
Penelope Weinberger, AASHTO, Pweinberger@aashto.org
CTPP Oversight Board
The CTPP Oversight Board met on August 25
and 26, 2010. The meeting was chaired by new
Oversight Board Chair Jennifer Finch, Colorado
DOT. Jennifer Finch is the Director of the
Division of Transportation Management and
Planning at the Colorado DOT. During the
meeting, the draft Mid-Program Report was
rolled out. The AASHTO CTPP 2008 to 2012
program is at its midpoint, and highlights of
achievements, remaining work, and remaining
budget are detailed in the report. The report will
be released in late January 2011 and posted on
the AASHTO CTPP web site. Highlights

include the availability of $1.4 million
remaining to commit to CTPP research, training,
and data needs as seen fit by the Oversight
Board. The next Oversight Board meeting is
scheduled for February 2011.
CTPP Training
1. Live Training
AASHTO has participated in a number of conferences and workshops and more are planned.
See the listing below for scheduled training.
The CTPP program team is always interested in
increasing the data users’ capacity to use CTPP
products. Please contact Penelope Weinberger
to discuss your training needs.

January 2011
Training Date

Page 5
Venue

Training Format

Training Staff

January 23, 2011
TRB Annual Meeting
9:00 a.m.-12:00 p.m.

Conference Workshop

February 1, 2011

Michigan State DOT and MPOs Training

In-person presentations Ed Christopher

February 2011

Florida Model Task Force

In-person presentations Ed Christopher and
Liang Long

February 25 and
February 28

TAZ Delineation Software Training for
All MPOs and State DOTs

Webinars

FHWA, AASHTO,
and Census Bureau

March 21, 2011

Arizona DOT TAZ Delineation and Data
Access Software Training

Hands-on computer
software training

Ed Christopher and
Liang Long

May 8, 2011

TRB Planning Applications Conference

Workshop

Elaine Murakami
and Ed Christopher

2. Electronic Training
Five webinars are archived and accessible on the
AASHTO CTPP webpage:
http://ctpp.transportation.org/Pages/
webinardirectory.aspx. Five eLearning modules
are developed or under development and will be
made available at:
http://ctpp.transportation.org/Pages/elearning
modules.aspx. The five topics covered are:
1. Census Transportation Planning Products
(CTPP) Based on American Community
Survey (ACS) Data;
2. The American Community Survey (ACS) as
it relates to CTPP;
3. What makes ACS CTPP tables different
from Long Form CTPP tables;
4. Geography; and
5. Margins of Error and Standard Error.
CTPP Five-Year ACS Data Products
The first CTPP using ACS with small area
tabulation will use ACS records from 20062010. AASHTO has been working with the user
community to develop a table request.
AASHTO is now working with Westat (the
contractor for the NCHRP Project 08-79,
“Producing Transportation Data Products from
the American Community Survey that Comply
with Disclosure Rules”) to generate a final

FHWA, AASHTO,
and Census Bureau

request. The data are expected to be released in
2012.
CTPP Web Site: http://ctpp.transportation.org
Data Conference
AASHTO’s CTPP program is jointly sponsoring
TRB’s Using Census Data for Transportation
Applications Conference. AASHTO’s partners
are FHWA, FTA, and RITA. The Conference is
scheduled to be held October 27-29, 2011 at the
Beckman conference center in Irvine, California.
Calls for papers, posters, and sessions will be
developed based on the following conference
objectives:
•
•
•
•

Disseminate the results of current research
focusing on gaps between needs and
products;
Share practitioner experiences using census
and other data sources;
Define strategies for practical improvements
in data use for current and emerging data
needs; and
Identify resources and approaches needed,
including funding, staffing and training, and
dissemination and accessibility to data.

We expect the conference to be an excellent
resource to the transportation data user
community.

Page 6

January 2011

Commutation Flow: CTPP 2000, ACS and CTPP, and LEHD-OTM
Nathan Erbaum, New York State DOT, Office of Policy Planning and Performance,
mailto:nerlbaum@dot.state.ny.us
Presently, the New York State Department of
Transportation (NYSDOT) has three sources
available on commutation flow:
1. The 2000 Census Transportation Planning
Package (CTPP) based on the decennial
Census Long Form, about 17 percent of
housing units;

attractive for zonal analysis, especially since it is
updated regularly. However, as they say, “the
devil is in the details.” Several issues with
LEHD-OTM already have been identified:
•

Accuracy of workplace location. FHWA
has noted that a home office is often
reported for all workers, rather than individual locations (multiple work sites)
(http://www.fhwa.dot.gov/planning/census/
lehdonthemap.htm). For example, this
occurs for school district with its various
local schools, or a supermarket chain with
many retail locations. The employment
location for an individual may show up as
the home office so the workplace location
maybe inaccurate.

•

Assignment model based on data from
Minnesota and documentation on validation
of this model to other states cannot be
found. Minnesota requires employers to
fully report workplace locations for businesses with multiple work sites.

2. Census Transportation Planning Program
(CTPP) based on the American Community
Survey (ACS) three-year file 2006-2008,
approximately seven percent housing units
in the sample over three years; and
3. Longitudinal Employment Household
Dynamics On-the-Map (LEHD-OTM),
which is available annually, based on the
Quarterly Census of Employment and
Wages (QCEW) (formerly ES202) and other
administrative records.
Each of these three datasets presents a challenge
to the transportation community in terms of
which snapshot of commutation flow best meets
our needs and is the most representative. The
Census 2000 Long Form and the ACS are sample surveys of housing units and include all
workers who went to work. Because of vacations, illness, and other temporary absences, it is
estimated that workers “at work” may be about 2
percent lower than a count of all workers, and
about 6 percent of workers have multiple jobs.1
The LEHD-OTM uses QCEW which uses
administrative records of workers covered by
unemployment insurance, and does not include
self-employed and some other classes of workers, estimated at about 10 percent of all
employment. There is an increasing demand for
data at detailed geographic granularity, and survey data with small samples may not be sufficient to meet that need.
The lure of LEHD-OTM is that it provides data
for home and work pairs synthesized down to
the block-level flow and is, therefore, very

1

Chuck Purvis in CTPP Status Report (May 2003)
http://www.fhwa.dot.gov/ctpp/sr0503.htm
(accessed 12/23/2010).

Today, the Internet enables us to easily access
data through Google searches or web interfaces
such as American Fact Finder (AFF) or LEHD
on the Map. But the ease of finding data is not
matched with finding caveats about the data
source. Sadly, it is this author’s observation that
ease of access to information via the Internet
may be causing a problem because people
assume that the data are correct and bypass any
documentation.
We decided to conduct a review of the 2006
LEHD-OTM and compare it with other sources,
including the CTPP2000 and the 2001 NHTS.
A number of specific tests were done to look at
the flow for each county from the top 5, 10, and
15 originating counties. When comparing the
LEHD-OTM to the CTPP 2000 findings
included:
•
•

The top origin/destination pairs for many
counties did not match.
The internal county flows were often much
lower in the LEHD-OTM compared to the
CTPP2000, even after adding in an

January 2011
estimated 10 percent of self-employed, who
were assumed to be more likely to work in
their own county.
When comparing the LEHD-OTM to the 2001
NHTS:
•

The 2001 NHTS has about 15 percent of
home-to-work trips exceeding 20 miles.
The LEHD-OTM has a much larger proportion of home-to-work pairs exceeding 20
miles.

Usual county-to-county flow pairs from the
LEHD-OTM which were not observed in the
1990 or 2000 CTPP suggested that the results in
New York State had a similar problem with
reporting of home and district office for the
reporting of employment.
Based on these differences, a proposal for further examination of the LEHD-OTM home-towork flows in other states besides New York
was submitted to the NCHRP 08-36 program.
This proposal was selected for funding, and
Task 98 currently is underway by Cambridge
Systematics.
In late August 2010, the CTPP three-year file
which uses 2006-2008 ACS became available.
NYSDOT decided to examine how the threeyear data compared with the flow data it had

Page 7
posted on its web site for the 1990 and 2000
CTPP https://www.nysdot.gov/divisions/policyand-strategy/darb/dai-unit/ttss, under the
heading Journey to Work Interactive
Application. This webpage was developed to
assist our regional staff in easily accessing the
Journey to Work data.
We decided to compare the three sources of
county-to-county worker flows. Comparing
Census 2000 with the CTPP 2006-2008 estimate
of flow requires the use of the Margin of Error
(MOE) because the ACS sample is so small
compared to CTPP2000. In reality, the MOE for
the CTPP2000 flow data also should be used.
Perhaps the LEHD-OTM also should include an
MOE measure, since it is a synthetic universe
based on QCEW, combined with administrative
records, with model-based assignments of
matches between workers and business establishment addresses. But unfortunately, this is
not available either. It would be best if we were
able to provide a convergent validation between
the sources that would give a snapshot of the
data so the elements that do not match could be
culled out and further analyzed. The CTPP
2006-2008 is limited to counties with over
20,000 population, compared to CTPP2000
which covers all counties. Figure 4 shows some
results of the comparison across three data
sources for Queen County, New York.

Figure 4. Sample Results of Journey to Work Flow Comparison – Queen County, New York

Why is such a three-way comparison necessary?
When methods are complex, different, and
sources as well as definitions vary, how these
factors impact the results is more important to
people than their methods of construction. If a

data point looks right (as in agreeing with CTPP
2000), or if the differences are perceptibly low,
then one can conclude that the data are correct.
However, if the opposite is true, than this also
must be checked.

Page 8
While NYSDOT was in the process of analyzing
these three data sources, we learned that one of
our metropolitan planning organizations (MPO)
was in the process of updating their regional
transportation model. Their consultant was
using the LEHD-OTM data and was
experiencing some issues with trip generation
and assignment to the network. The mere fact
that they were encountering problems in the
block-level detail that LEHD-OTM could provide suggested that at a minimum, some comparison should be undertaken to illustrate where
the flows seemed to be comparable and where
there were significant discrepancies. The comparison process enables us to shine a light on
where things work, and also where they do not
work, and enables people to ask questions about
the reasons the numbers are different. We must
rely on available data. Therefore, having a full
understanding of how well it works can shine a
light on any problems that may need to be fixed.
NYSDOT’s web link to this comparison analysis
is located here:

January 2011
https://www.nysdot.gov/divisions/policy-andstrategy/darb/dai-unit/ttss/cttp_acs.
Most of the relevant caveats are listed towards
the bottom of the page.
We found that although the counts may vary,
when the O&D analysis was done as proportional shares, the data looked more comparable.
Therefore, one of our recommendations is that
using proportional shares to compare across
these data sets may be more useful than
comparing counts of workers. We should keep
in mind that people often inquire about size,
share, and change for many measures. We are
often asked for comparative data; for example,
what is the commutation flow between Queens
and Manhattan, how does it compare with the
other counties within NYC, and how has the
value changed over time. The issue of assuring
that the data are reliable, representative, and can
be used must be demonstrated. Equally important is that the end users need to understand the
impact of small samples on their decisions.

CTPP and ACS Schedule
Ed Christopher, FHWA Resource Center Planning Team, edc@berwyned.com
Data Product

Planned Release Date

Three-Year CTPP (2006-2008 Data)

January 2011

Three-Year ACS (2007-2009 Data)

January 2011

2010 TIGER Files (new Block, Block Group, and Tracts)

Flow Basis completed by end of February 2011

2010 Census Population Counts for All Census Geography
(PL 94-171)

By April 1, 2011

TAZ/TAD Delineation Software Deployed

March through April 2011

TAZ/TAD Delineation Completed

June to early July 2011

2010 Census Summary File 1

June to August 2011

New PUMAs Defined

Fall 2011

ACS (2010), ACS (2008-2010), and ACS (2006-2010)

Fall 2011

New Urban Areas Released

Spring 2012

Five-Year CTPP (2006-2010)

Fall 2012

TIGER with Urbanized Areas and Urban Clusters

Fall 2012

January 2011

NCHRP 08-36, Task 98 – Improving
Employment Data for Transportation
Planning
Bruce Spear, Cambridge Systematics, Inc.,
bspear@camsys.com
Project Overview
High-quality employment data, including
workplace location, industry type, and number
and geographic distribution of workers, are critical to transportation planning and policy analysis. For several decades, transportation planners
have relied heavily on journey-to-work data
collected as part of the decennial Census Long
Form to obtain workplace location and distributions of home-to-work trips. However, the
replacement of the 2010 decennial Census Long
Form questions by the continuous sample
American Community Survey (ACS) has raised
concerns within the transportation planning
community about the adequacy of the sample
size to provide reliable data on workplace locations and home-to-work flows. Consequently,
alternative data sources are being examined.
Two public sources of employment data are the
Bureau of Labor Statistics’ (BLS) Quarterly
Census of Employment and Wages (QCEW),
and the Census Bureau’s Longitudinal Employer
Household Dynamics “On the Map” (LEHDOTM) data. Although neither of these databases
were developed specifically for transportation
planning purposes, they each hold significant
promise. However, many potential users in the
transportation community are unfamiliar with
these data sources, and lack key information on
how the data was collected, limitations and
caveats on use, or even where to obtain the data.
The purpose of this research study is to develop
a guidebook that provides key information for

Page 9

NHTS Version 2.0 Released
The Federal Highway Administration
announced the enhanced 2009 NHTS data
(Version 2.0) in November 2010. The
enhanced NHTS data features improved
methods of processing outliers and
population controls using the 2008
American Community Survey.
The Version 2.0 data file is now available
for download on the On-Line Analysis
Tools page at http://nhts.ornl.gov/. The OnLine Codebook Browser has been updated
and the User’s Guide is available at the
Publications page at http://nhts.ornl.gov/.

transportation planners on the QCEW and
LEHD-OTM data with respect to how they are
collected, how to access and use the data, and
their uses and limitations for transportation
planning applications. Additionally, the guidebook will identify opportunities for improving
the underlying data.
The research study is approximately halfway
completed, with a scheduled completion date of
July 2011. Work to date has focused on:
1) a comparative review of publicly available
QCEW and LEHD-OTM data products;
2) preparing for interviews of selected state
employment security agencies regarding current
agreements and issues in sharing more detailed
employment data with other state and local
agencies, particularly state DOTs and MPOs;
and 3) creating a nationwide county-to-county
database of home-to-work flows from the
LEHD-OTM.

Page 10

January 2011

CTPP Hotline – 202/366-5000

E-mail: ctpp@dot.gov
CTPP Listserv: http://www.chrispy.net/mailman/listinfo/ctpp-news
CTPP Web Site: http://www.dot.gov/ctpp
FHWA Web Site for Census Issues: http://www.fhwa.dot.gov/planning/census
2005-2007 ACS Profiles: http://ctpp.transportation.org/profiles_2005-2007/ctpp_profiles.html
AASHTO Web Site for CTPP: http://ctpp.transportation.org
1990 and 2000 CTPP Data Downloadable via Transtats: http://transtats.bts.gov/
TRB Subcommittee on Census Data: http://www.trbcensus.com
AASHTO
Penelope Weinberger
PH: 202/624-3556
E-mail: pweinberger@aashto.org

FHWA
Elaine Murakami
PH: 206/220-4460
E-mail: elaine.murakami@dot.gov

Jennifer Finch,
Chair, CTPP Oversight Board
PH: 303/757-9525
E-mail: jennifer.finch@dot.state.co.us

Ed Christopher
PH: 708/283-3534
E-mail: edc@berwyned.com

Jonette Kreideweis, MN DOT
Vice Chair, CTPP Oversight Board
PH: 651/366-3854
E-mail: jonette.kreideweis@dot.state.mn.us
Census Bureau: Housing and Household
Economic Statistics Division
Alison Fields
PH: 301/763-2456
E-mail: alison.k.fields@census.gov
Brian McKenzie
PH: 301/763-6532
E-mail: brian.mckenzie@census.gov
FTA
Ken Cervenka
PH: 202/493-0512
E-mail: ken.cervenka@dot.gov

Liang Long
PH: 202/366-6971
E-mail: liang.long@dot.gov
TRB Committees
Catherine Lawson
Urban Data Committee Chair
PH: 518/442-4773
E-mail: lawsonc@albany.edu
Clara Reschovsky
Census Subcommittee Co-Chair
PH: 202/962-3332
E-mail: creschovsky@mwcog.org
Kristen Rohanna
Census Subcommittee Co-Chair
PH: 619/699-6918
E-mail: kroh@sandag.org

CTPP Listserv
The CTPP Listserv serves as a web-forum for posting questions, and sharing information on Census and
ACS. Currently, over 700 users are subscribed to the listserv. To subscribe, please register by
completing a form posted at: http://www.chrispy.net/mailman/listinfo/ctpp-news.
On the form, you can indicate if you want e-mails to be batched in a daily digest. The web site also
includes an archive of past e-mails posted to the listserv.