a product of the CTPP Working Group firstname.lastname@example.org
What Does the Transportation Community Need to do?
Out for Review
What's Happening With It?
Salem-Keizer (OR) MPO Area
Message from the
Draft CTPP 2000 Content
Ready for Review
By Sherry Riklin, Federal Transit Administration
We have posted the proposed tabulations in Adobe pdf format to the CTPP
Website. We encourage your comments on the proposal. To access the
documents, please visit:
The website contains
1. A listing of the proposed tables.
2. A summary of the rationale we used to identify specific tables.
3. A description of the variables that are included in the tables.
Several improvements to CTPP are being proposed. The three sets of standard tables: Home End tables, Work End tables and Worker Flow tables, will be organized by topical content. New tables have been added to help planners address such issues as jobs access and environmental justice. In addition, we are also considering the possibility of providing custom tabulations.
The questions on the Census long form utilized in the CTPP cover topics such as household size, auto-ownership, income, work place location, means of transportation to work, carpool occupancy, time leaving home to go to work, and travel time to work. Data from these questions and the general questions on race, Hispanic origin, occupation and industry comprise the characteristics for the tables in the package.
Your suggestions are very important to us. To send your comments, please contact Nanda Srinivasan by calling 202-366-5021 (e-mail email@example.com) by August 15, 2000.
Public Use Microdata Sample (PUMS)
PUMS contains records for a sample of housing units with information on the characteristics of each unit and each person in it. While preserving confidentiality (by removing personal identifiers and detailed geographic codes), these microdata files permit users with special needs to prepare virtually any tabulation.
The Census Bureau is considering several changes to the decennial census PUMS. The proposed changes are designed to reduce the potential for disclosing individual information, i.e., to protect confidentiality.
The Disclosure Review Board (DRB) within the Census Bureau has determined that only a ?6 percent file? can be released in the PUMS. Six percent of the population in PUMS translates into approximately one-third of long form records.
The Census Bureau?s current proposal is to provide grouped or rounded values instead of individual answers for age over 75, occupation, industry, ancestry, place of birth, language, income, earnings, travel time to work, and departure time to work. The potential concern to transportation planners is that the proposal is for travel time to work to be rounded to five-minute intervals, and departure time to work to be rounded to 15-minute intervals. For more information on the Census Bureau proposals, please visit the IPUMS website at http://www.ipums.umn.edu/~census2000/classifications.html
Public Use Microdata Area (PUMA) definition
The Census Bureau proposal includes maintaining 100,000 as the population threshold for PUMAs in the state-level PUMS. This is a very important decision and is strongly supported by the transportation community. The timeframe for designating the state-level PUMAs will be after the release of the population counts at the block level from the PL 94-171 data (after April 1, 2001). The process for defining PUMAs will be through the Census Bureau State Data Centers.
Issues that affect transportation planning
Several transportation programs use PUMS data. For example, TRANSIMS is a microsimulation project being developed by DOT, EPA, with technical work conducted by the DOE Los Alamos National Laboratory. This is a multi-year $40 million effort to replace the 40-year old four-step travel demand system. Because it is a microsimulation, it relies on microdata at the front end to populate household characteristics along street segments. For such micro-simulation purposes, we need to have as many records in PUMS to use as possible. Once the street segments are populated with persons in households, then personal travel activities are simulated and then the appropriate trips are simulated through the transportation network. Ultimately, traffic congestion and vehicle emissions are estimated. It is critical that a large microdata file is available that includes age, gender, earnings, household income and number of vehicles, travel mode to work, travel time and departure time.
The census will make decisions on PUMS within the next two to three months. It is important for transportation planners to voice their concerns to the Census Bureau on this valuable data source. The CTPP Working Group is planning to have letters regarding PUMS sent to the Census Bureau from the Director of the Bureau of Transportation Statistics (BTS), and from the AASHTO Standing Committee on Planning.
A copy of the BTS letter on PUMS can be found on the CTPP Website at:
To submit input to the Census Bureau, please write to:
Paula J. Schneider
Principal Associate Director for Programs
Bureau of the Census
Federal Office Bldg. 3, Room 2037
4700 Silver Hill Road
Suitland, Maryland 20233
Also, the Task Force on the 2000 PUMS would like to receive copies of
any relevant PUMS correspondence:
CTPP data have also been used for examining inter-city flows between Salem and surrounding cities. Salem is the state capital and the regional economic center,
and about thirty percent of all workers commute from outside the metropolitan area to jobs located in Salem. The CTPP data were particularly useful in a recent bridge study which called for examining commuting patterns across the bridges into downtown Salem. Planners and elected officials wanted to know the residence characteristics of commuters who used the bridges and worked in the Capitol Mall area. The CTPP data was used to provide answers for the bridge study. The bridge study can be found in the publication entitled "Willamette River Crossing Capacity Study, Draft Phase I Report, Salem-Keizer Area Transportation Study, March 1999."
The modeling and the bridge study were both done in-house. For more
questions on the bridge study or the use of CTPP data in Salem, please
Mike Jaffe, Senior Transportation Planner
Phone: 503-588-6177 fax: 503-588-6094
What is the American Community Survey (ACS)?
The 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. 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 is being conducted in thirty-one 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.
When will nation-wide data from ACS be available?
The table below lists data availability for different areas. The ACS data from the test sites will be available from the middle of July this year. The earliest data from the fully implemented ACS is expected to be available in 2004 for areas of population greater than 65,000.
Census Bureau Sponsored Conference on ACS – June 6-7, 2000
The Census Bureau sponsored a conference on "Developing Public Policy Applications with Community Administrative Records and the American Community Survey" in Baltimore, Maryland on June 6-7, 2000. There were roundtable discussions with the data user community on several broad-ranging topics including:
1. Data Integration Strategies.
2. Predictive Modeling.
3. How to integrate the ACS and decennial Census data into time series modeling.
4. A web-based interactive system for rural America.
5. Development of GIS to enhance community information systems.
Some of the issues raised were
|1. Confidentiality Issues
Attendees felt that cutting geographic or tabular detail may not be the only way to maintain confidentiality.
The Census Bureau should investigate other methods such as data swapping, introducing noise, development of a ?synthetic? database, etc. as other means of disseminating useful data at lower levels of geography.
|2. Administrative records
On the issue of aggregating local administrative files to the same geographic units as census and combining variables to calculate rates, attendees felt that:
a. There is a lack of consistency in
data definitions by state and local governments.
Attendees felt the Census Bureau should evaluate various applications of decennial and ACS data and develop a database of the ACS user community. This would allow better understanding of user needs. An ACS listserve should be considered in addition to the existing ACS website.
|4. Data Access and Documentation
Data dissemination should contain data dictionaries indicating what kind of analyses are possible with the data in terms of spatial and temporal accuracy, difference between counts and estimates, mapping uncertainties, and error propagation.
|5. Education and Training
The Census Bureau needs to develop and disseminate training materials to the user community on applications and uses of ACS data.
|6. Methods and Tools
Census Bureau should develop and share methods and tools especially with respect to spatial analysis of ACS data.
What are the issues for the transportation planning community?
|1. Workplace/Employer Coding
In the test cases, ACS data has been coded only to county/place. The workplace data from ACS needs to be geocoded to census block and TAZ geography using a current employer location file. Since this will need to be done on a continuous basis, Census Bureau will need to develop a mechanism for this process and determine whether a mechanism for local participation can be included.
|2. Effect of Seasonal Variation
Since the ACS is a continuous survey, there needs to be research on the impact of seasonal differences on travel characteristics. Typically, household travel surveys are conducted in Spring/Fall. April 1 for decennial census matched well with ?Spring? data collection efforts.
|3. Reporting Travel Characteristics
The transportation planning community faces several issues. The following are a few of the issues that need to be studied:
a. How should travel time, income, etc.
be reported in a special transportation planning package with ACS.
Should there be an annual CTPP for large geographic units? Should there
be a system for access to microdata?
The ACS data for the test sites offers a unique opportunity to examine and compare ACS with CTPP 2000 for comparative time periods. The test site data need to be examined more closely. The ACS data for the 1996, 1997, and 1998 sites have been released (1999 data is due in the middle of July). For more information on ACS please visit the Census Bureau website at http://www.census.gov/acs/www
In 1996, the Bureau of Transportation Statistics conducted a study entitled ?Implications of Continuous Measurement for the Uses of Census Data in Transportation Planning”. This report presents the findings of an expert panel on the utility of data obtained from continuous measurement for transportation planning. Copies of the printed report can be obtained by sending an e-mail to firstname.lastname@example.org.
On a related front, in May the subcommittee submitted a proposal to
the Transit Cooperative Research Program (TCRP) for consideration.
This proposal called for the development of training materials to assist
transit planners in the use of census and other federal statistical data.
The proposal focused on the use of CTPP, PUMS and
ACS for transit planning applications. A copy of this proposal can be found at http://www.TRBcensus.com/notes/tcrp052000.html
(At press time I learned that the project was not funded. Needless to say this was quite a disappointment.)
On a brighter note, the subcommittee has requested a timeslot at 2001 TRB annual meeting for a presentation session. At the session we plan to cover PUMS, ACS, AHS and the CTPP with a focus on applications. This will allow time at the subcommittee meeting to discuss data and research needs. Although the TCRP proposal was not selected during this funding cycle, using Census data for transit planning applications is still important.
If anyone is working on any research or has a planning application that uses Census data, please pass the information along. The sub-committee is always looking for planning applications and current research.
On a final note, I have now become a "real" federal employee. On May 8, 2000, I accepted a full time position with the Bureau of Transportation Statistics within the US DOT. After almost 20 years at the MPO in Chicago (CATS), I decided to see the world from a different perspective. My duties include state and MPO outreach so I plan to be involved in local and state data issues as much as ever. My contact information can be found elsewhere in this Status Report.
Chair, TRB Subcommittee on Census Data for Transportation Planning
The CTPP listserv is an important source of information on CTPP 2000
and other decennial
To subscribe to the CTPP Listserv, send an e-mail to email@example.com
You can also find up-to-date information on CTPP 2000 on the Internet
|"Surf's Up" Web Sites to Remember|
|Ed Christopher (Census Subcommittee Chair)
|Chuck Purvis (Urban Data Committee Chair)
|Ed Limoges (Census Subcommittee Secretary)
|Ron Tweedie (State Data Committee Chair)
Census Population Division (JTW questions)
Census Geography Division (for TAZ-UP questions)
(See under TRB Committees)
BACK to Home