In the video, we want to highlight three organizations which can showcase how they plan to use the data, with each organization discussing more than one application of the data. One example might be a State DOT who will be using it for: statewide planning, corridor analyses, and assisting smaller MPOs with travel demand models. Please send an email to ctpp@fhwa.dot.gov if you have any ideas or if your agency would like to be considered for the video.
1. Kentucky Statewide Modelers
Group Meeting in Louisville, KY ; October 17, 2000.
2. TRB Performance Measures
Conference in Irvine, California; October 29, 2000
3. IPG Meeting in San Diego;
November 5 - 7, 2000.
4. 80th Annual Meeting of
the Transportation Research Board in Washington DC, January 7- 11, 2001.
Please plan to meet the CTPP Working Group members to share your ideas and concerns if you are planning to attend any of the meetings listed above.
Since then, the Census Bureau assigned Phil Salopek to work with the U.S. Department of Transportation (USDOT) to address the concerns that were presented to Dr. Kenneth Prewitt, Director of the Census Bureau by Dr. Ashish Sen, Director of the Bureau of Transportation Statistics (BTS).
To protect individual confidentiality, the Census Bureau is generally using two approaches to reduce the chance of disclosure for continuous variables. These are:
1. For continuous variables, choose the top-coded value so that the category contains at least 0.5% of the total US population. and;The USDOT has now submitted to the Census Bureau a specific proposal for categories for travel time and departure time. They are:2. For categorical variables, grouping values if there are fewer than 10,000 cases nationwide in any specific category.
Departure time: (military time)
We thank those of you that responded to the CTPP listserv. We hope that our suggestions are taken into account when the final decisions for the PUMS file are made.
Many MPOs, however, have continued to find that CTPP data enhances their vehicle availability forecasting process. The CTPP information can aid in developing, validating, and applying vehicle availability models. For more detail and background on vehicle availability modeling, the reader is encouraged to read the report, “Vehicle Availability Modeling” prepared by Cambridge Systematics, Inc. for FHWA in May 1997. (http://www.bts.gov/tmip/papers/surveys/vam.pdf).
Substitute where disaggregate (individual/household data) are not
available
Many early models on vehicle availability were developed from
Census data at the small-area level; these types of models can still be
developed for regions which do not have a recent travel survey to provide
data on individual households. Using CTPP data and regression procedures,
average vehicle availability by zone can be related to zonal average values
of variables such as household income, number of persons, and number
of workers. With the addition of acreage of TAZs, these models can
also be extended to include population, household, and/or worker density
variables.
Alternatively, the dependent variables can be the shares of households in a zone which have a specified number of vehicles available – the shares of households, for example, with zero, one, two, and three or more vehicles. Models of this type cannot reflect the unique behavior of individual households, but may be sufficient in regions with highly homogenous populations, or as preliminary models until detailed recent household survey data are obtained.
Accessibility Measures
CTPP can provide zonal characteristics that are used in combination
with individual household data for vehicle availability models. Some examples
of zonal characteristics are population density and employment density.
Using a Geographic Information Systems (GIS), these variables can be transformed
into accessibility measures when combined with a transportation network.
Categorical Data Beyond Averages
The CTPP is valuable because it can provide not just the average vehicle
availability for a zone, but the shares of households with 0, 1, 2, 3,
4+ vehicles. This is critical information for regions that need to have
trip generation or mode choice models for each category of vehicle availability.
Model Validation
CTPP data becomes the most valuable for the validation step of vehicle
availability modeling. By comparing predicted vehicle availability
shares and averages with CTPP data, model developers can determine the
accuracy and sensitivity of their models, and identify the need for additional
model variables. Tabulations of the model results for individual
households by income level, household size, and numbers of workers, for
example, can be compared directly with CTPP tables for the entire region
and for selected subareas. Variations between the predicted and observed
data help to identify the need for additional model variables or for revised
forms of variables – an example would be changing from a simple household
income variable to a logarithmic form to reflect the reduced importance
of changes in income levels as household income increases. Comparisons
can also be made of observed and predicted information by zone or district
to identify biases related to geographic factors not accounted for in candidate
models. The CTPP data allows these types of validation checks to
be made more readily, since the longform sample of 1 in 6 households nationwide
is much greater than that of MPO’s household travel surveys (generally
less than 1 percent of households).
The reported variation between a commute on a ‘usual’ day and any specific day is not great for people who usually commute by private vehicle. However, for those who usually use transit or walk to work, over twenty percent are likely to use a private vehicle to commute on any particular day. This shows that using transit for work trips reflects an increasing proportion of workers for whom transit is used as a choice, and they are not captive to it.
Mode of Travel on Travel Day for Workers Making a Commute
Trip
Compared to “Usual Mode” (Compiled using 1995 NPTS)
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Improvements for the 2000 Survey
One of the goals for the 2000/2001 survey is to improve the data on
both short trips (walk and bike) and mid-range distance trips (50 to 100
miles). We are asking people to remember trips 50 miles or more over
the last month in addition to a 1-day travel diary.
We have also added questions on telecommunications, because it is important to understand how these technologies are influencing our daily travel. The NPTS pretest found that over 30 percent of the households had more than one telephone line, and 58 percent percent of the households had at least one cell phone.
Add-on Fever
The add-on program allows local jurisdictions to purchase additional
samples of the NPTS in their area. To date, three States and eight
MPOs have expressed serious interest in purchasing add-on samples–adding
almost 60,000 households to the sample. In the 1995 NPTS, the State
of New York and the Commonwealth of Massachusetts, and 4 MPO add-ons, represented
an additional 21,000 households to the sample.
Some States and MPOs do not have the time and resources to develop, contract, and manage a household travel survey. This project allows States and MPO to use State Planning and Research (SP&R) or Planning (PL) funds and waives the requirement of local match. The additional samples are compiled, geocoded, and edited and weighted to represent the participating region.
In addition to the traditional travel diary, a vehicle-based GPS component is also an option with the add-on program. So far, two areas are considering this option. The GPS unit would stay in the vehicle for a week or two, overlapping the one-day diary. Such a concurrent data collection allows the number of trips counted by the machine to be compared to the number reported by telephone respondents, and to compare GPS-measured VMT to reported VMT. Using a 7-14 day survey period will also provide data to analyze the daily variation in travel, examination of travel speed along routes, and has the potential for sophisticated route-choice analysis.
For more information, please visit the NPTS website at: http://www-cta.ornl.gov/npts
The other research-oriented project, that we thought was dead, actually is alive and kicking. It was submitted to TCRP in May and this past July a group of transit professionals met and screened over 120 proposals. Our project, "Census Data for Transit Planning" made it though the screening process and will go before the TCRP Oversight and Project Selection Committee for consideration. The project scope can be found at http://www.TRBcensus.com/notes/tcrp052000.html
This past August, our parent committee, the Committee on Urban Data and Information Systems held its mid-year meeting in Madison, Wisconsin. At that meeting we discussed plans for a presentation session at the TRB Annual Meeting in January 2001. Our session will consist of four presentations on the application of Census data products for transportation planning. Presentations are tentatively slated on the American Housing Survey, use of the decennial census Public Use Microdata Sample (PUMS), the American Community Survey, the North American Industry Classification System, and an update on the CTPP. Check the TRB web site for further details, http://www.nas.edu/trb/
In Madison we also discussed what, if anything, could be done to encourage
those states and MPOs with American Community Survey (ACS) test counties
to begin looking at their ACS data. This will become especially important
as decennial census products begin to be released. Remember that
the reason for the three-year test cycle of the ACS was to be able to benchmark
the ACS data against the decennial data. To find out if you have
a test ACS site area near you go to the ACS website at http://www.census.gov/acs/www/
or you can go directly to the ACS test sight listing at
http://www.census.gov/acs/www/html/meth_doc/overvw99.htm
See you in January at the TRB Annual
Meeting (January 7-11, 2001).
(Subcomittee meeting and conference session date and time tbd)
Ed Christopher,
Chair, TRB Subcommittee on Census Data for Transportation
Planning
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TRB Committee on Travel Survey
Methods (A1D10)
by Elaine
Murakami, FHWA
For basic information about travel surveys, I recommend the Travel Survey Manual (FHWA-PL-96-029), completed in 1996 through the Travel Model Improvement Program (TMIP). To order a copy, please FAX your request to the FHWA Report Center at 301-577-1421 (phone number 301-577-0818). Please be sure to include the FHWA publication number, and your full mailing address and phone number.
NHI course, "Development and Implementation of Travel Surveys" is now available. The course is currently scheduled for November 14-16 in Des Moines, Iowa; and December 4-6, in Las Vegas, Nevada. Please use the TMIP webpage, under "Courses" for more information: www.bts.gov/tmip/tmip.html
Conference proceedings from an International conference on Transport Survey Methods held in 1997 were just released on the TRB webpage: www4.nationalacademies.org/trb/onlinepubs.nsf/web/circular This is an excellent document which addresses many issues which perplex transport surveys in the United States and around the world, and provides ideas on improving the quality of these surveys.
The committee is sponsoring a Roundtable on Personal Travel Surveys. The objective of the Roundtable is to bring together people from the survey methods and transportation communities to provide the USDOT with ideas about research to improve national surveys on personal travel behavior. This group convened, for the first time, on September 21, 2000.
For more information about TRB Committee A1D10, please see the committee webpage at: ww.fhwa.dot.gov/ohim/trb/trbpage.htm
| "Surf's Up" Web Sites to Remember | |
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| Ed Christopher (Census Subcommittee Chair)
PH: 202-366-0412 FAX: 202-366-3640 EdC@TRBcensus.com |
Chuck Purvis (Urban Data Committee Chair)
PH: 510-464-7731 FAX: 510-464-7848 cpurvis@mtc.ca.gov |
| Ed Limoges (Census Subcommittee Secretary)
PH: 313-961-4266 FAX: 313-961-4869 limoges@semcog.org |
Ron Tweedie (State Data Committee Chair)
PH: 518-457-1695 FAX: 518-457-8317 rtweedie@gw.dot.state.ny.us |
Census Population Division (JTW questions)
| Phil Salopek
PH: 301-457-2454 FAX: 301-457-2481 phillip.a.salopek@census.gov |
Clara Reschovsky
PH: 301-457-2454 FAX: 301-457-2481 clara.a.reschovsky@census.gov |
Census Geography Division (for TAZ-UP questions)
| Jamie Rosenson
PH: 301-457-1099 FAX: 301-457-4710 jrosenson@geo.census.gov |
Valerie Murdock
PH: 301-457-1099 FAX: 301-457-4710 vmurdock@geo.census.gov |
Bob LaMacchia
PH: 301-457-1022 FAX: 301-457-4710 rlamacchia@geo.census.gov |
FHWA
| Elaine Murakami
PH: 202-366-6971 FAX: 202-366-7742 elaine.murakami@fhwa.dot.gov |
Nanda Srinivasan
PH: 202-366-5021 FAX: 202-366-7742 nanda.srinivasan@fhwa.dot.gov |
Mark Sarmiento
PH: 202-366-4828 FAX: 202-366-3713 mark.sarmiento@fhwa.dot.gov |
FTA
| Jim Ryan
PH: 202-366-0954 FAX: 202-493-2478 james.ryan@fta.dot.gov |
Sherry Riklin
PH: 202-366-2419 FAX: 202-493-2478 Email: sherry.riklin@fta.dot.gov |
| BTS
Ed Christopher (See under TRB Committees) |
AASHTO
Deborah Buchacz PH: 202-624-5839 FAX: 202-624-5806 debbieb@aashto.org |
