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Message from the
CTPP 2000: Revised List of Part 3 (Worker Flow) Tables for Small
As the negotiations stand, the DRB has recommended that two tables, Table 3-1 (Total Workers) and Table 3-2 (Total Workers by Mode to Work--17 categories) be released without a minimum threshold. Tables 3-8 through 3-14 that present aggregate statistics, e.g. means, medians, aggregates, also could be released without a minimum threshold. However, Tables 3-3 through 3-7 would ONLY be released subject to a minimum threshold of 3 un-weighted records in the geographic flow pair e.g. TAZ-TAZ. In addition, all flow tables would be rounded.
Because the DRB has not made it clear what evaluative criteria it used for this determination, the CTPP Working Group is continuing its negotiations to determine if there are any other acceptable alternatives for obtaining flow tables without thresholds. The Working Group has submitted another query to the DRB and awaits their response. The DRB’s next meeting is scheduled for January 14, 2002.
Who/What is the DRB?
The DRB is comprised of Census Bureau staff who have the responsibility to ensure that individuals cannot be identified through published Census Bureau products.
BTS Director Ashish Sen writes to Census Bureau Acting Director William Barron
In response to the DRB’s initial determination that called for the minimum threshold of 50 unweighted records, Dr. Sen wrote to Mr. Barron explaining that limiting the release of information to this minimum threshold would make this data set essentially useless for transportation planning. Administrators Jennifer Dorn (FTA) and Mary Peters (FHWA) also sent a letter conveying their support of Dr. Sen’s letter. In response, a sub-group of the DRB was assigned to meet with the CTPP Working Group.
CTPP Working Group meets with DRB Subgroup
On the basis of the discussions with the DRB Subgroup, the CTPP Working Group submitted a revised set of tables that favor simple 1-way tabulations for counts, but also includes 2-way tables for summary measures (means, aggregates). The revised list, although considerably less comprehensive than the original CTPP 2000 request, includes tables that were not available in the 1990 CTPP.
Rounding is acceptable?
The DRB is requiring that all special tabulations from the decennial census use rounded values. Specifically for the CTPP, values between 1 and 7 would be rounded to “4”, and values 8 and over would be rounded to the nearest “5”. After examining 1990 CTPP data which was not rounded, rounding it and comparing the results of rounded and unrounded data, most members of the CTPP Working Group believe that rounded values will have little impact on the utility of the CTPP 2000 dataset.
|"Surf's Up" Web Sites to Remember|
Nanda Srinivasan is in the process of contacting all MPOs to update the CTPP agency database. If the contact information for your agency has changed, please send an e-mail to Nanda.Srinivasan@fhwa.dot.gov.
Prior to the CTPP, Summary File 3 will be released on a flow basis by state between June and September 2002.
CTPP Part 1 – Residence Based Tables
CTPP Parts 2 & 3– Work End Tables & Worker Flow Tables:
The CTPP will also be released by state.
The American Community Survey’s Census 2000 Supplementary Survey (C2SS) was a sample survey of 700,000 households conducted in 1,203 counties. Data was collected throughout the year 2000. In mid-August, the Census Bureau released C2SS data for states and the nation. In mid-November 2001, data for counties and places with populations over 250,000 were released. Like the decennial census, the C2SS provides information on three key elements of commuting activity: ownership of personal vehicles; travel mode to work, and travel time to work.
While C2SS data exhibit some methodological differences from the decennial data, it can be used for comparison for most purposes until the decennial data are available. The first long form data from the decennial census are expected to be released between June and September 2002. Because the C2SS samples are small, the error is relatively large compared to decennial census long form data, so please exercise caution when working with the data. Nonetheless, it is data from 2000, available now, and will probably give a good idea of what to expect from Census 2000 Summary File 3.
State and National data:
The CTPP Working Group conducted preliminary analysis of journey to work trends for the nation and states using data from the 1990 CTPP, and 2000 C2SS.
We found that:
1. Vehicle availability: For the nation, the percent of households with no vehicles decreased from 11.5% in 1990 to 9.3% in 2000.
2. Carpooling to work: Nationally, the percent of workers carpooling to work declined from 13.4 percent (1990) to 11.2 percent (2000) of all workers. The same trend was observed in most states.
To access the nation and state data from C2SS, and some transportation focused state summaries, please visit: http://www.trbcensus.com/c2ss.html
Place and County data:
The Metropolitan Transportation Commission, Oakland, California analyzed the C2SS data for the San Francisco Bay Area. Their analysis can be accessed at their website at:
The CTPP Working Group prepared some sample Journey to Work profiles using the American Community Survey C2SS data files. You can view the profiles on the internet at: http://www.trbcensus.com/c2ss/profiles.html
The C2SS is an experimental survey and is part of the testing for the American Community Survey. We are very interested in knowing about YOUR analysis with the C2SS data files or other American Community Survey products. Please share your analysis with the CTPP listserv by sending an email to: email@example.com
The year 2001 began quietly enough with our American Community Survey (ACS) proposal winding its way through the National Cooperative Highway Research Program process. While the project was not selected for funding in 2001-2002, it did make it to a contingency list, and was resubmitted through the 2002-2003 process. This time through, the Subcommittee secured support not only from the TRB data committees but also the AASHTO Standing Committee on Planning. With this added support we are optimistic that the project will make it through the selection process. A summary of the proposal can be found at http://www.TRBcensus.com/notes/nchrp_acs.html
This past August the Internet service provider where the Subcommittee’s web pages were housed went “belly-up”. As a result, a domain name was secured and a new site launched. The new web address is http://www.TRBcensus.com/. In addition to this location the CTPP Working Group within the US Department of Transportation (DOT) managed to secure a first level directory web address under the USDOT main page. The USDOT CTPP web address is http://www.dot.gov/ctpp/. With two Web sites we should see an even greater abundance of materials being posted. The intent of the two web sites is to allow CTPP specific materials to gravitate towards the USDOT maintained pages while the Subcommittee can broaden its sights to include other census data that is important to the transportation planning community.
Now that Census 2000 is complete, there are two things worth keeping an eye on. The first are the reports people will prepare examining the quality and methodological issues surrounding the census. The second area to watch for is the “cool” and “exciting” things people are doing with the data.
On the methodological front, the U.S. General Accounting Office in December 2001 released a report analyzing the costs for conducting the Census 2000. The study found, among other things, that the estimated full-cycle cost of the 2000 decennial census of about $6.5 billion was nearly double the $3.3 billion reported full-cycle cost of the 1990 decennial census. For a complete copy of the 27-page report go to http://www.gao.gov/new.items/d0231.pdf
The other things to look for are the new and innovative “stuff” that people are doing with the Census data. If you think back a short 10 years to our last decennial census you can see some very noticeable changes that have occurred. In 1991, many of us were still sharing computers and the idea of a PC on your desk with spreadsheet, mapping and statistical capabilities was only a dream. The ability to do online data searchers with services like the Census Bureau’s American Fact Finder (http://factfinder.census.gov/) and those offered by just about every major newspaper in the country was also a dream. The USA Today still has a good site to check http://www.usatoday.com/news/census/index.htm. In short, as our resource and computing ability have become more sophisticated, so have our products.
Other issues to keep a watchful eye on during the year include: the development of the CTPP especially as it relates to the Census Bureau’s Disclosure Review Board process and restrictions; the establishment of statewide TAZs; the definition of the areas that the urban CTPP components will cover; the new Census Urbanized Area boundaries (due out in March); and a series of outreach materials--a brochure and video to be released in early 2002 followed by an instructional electronic guidebook.
As these issues and many more unfold we need to hear from you. Many times members of the subcommittee and CTPP Working Group are called on for our collective opinions. One source for that information is the CTPP-News listserve. You can post to the listserve at firstname.lastname@example.org. To be added to the listserve just drop me an email at edc@TRBcensus.com.
So let’s hear from you!
Chair, TRB Sub-committee on Census Data for Transportation Planning
PH: 202-366-6971 (206-220-4460 in Seattle)
Ed Christopher (Census Subcommittee Chair)
|Census Bureau Geography Division
PH : 301-457-1099
FAX : 301-457-4710
|Census Population Division
|Chuck Purvis (Urban Data Committee Chair)
Ed Christopher (Census Subcommittee Chair)
See under FHWA
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