On your question #1: One thing to keep in mind relates to the fact that a
"HBW trip" for modeling purposes represents a trip end, e.g., a Home to Work
trip and a Work to Home trip would actually be counted as two separate
trips, i.e., HBW productions and two HBW attractions.
So, using your NCHRP example, 1,000 employees would generate 1,500 HBW
trips--but only half of these (750) would be comparable to a CTPP-derived
home-to-work trip.
In terms of why travel survey data never supports 2.0 HBW trips per
employee: It is partly because of absenteeism on an "average" weekday,
partly because some jobs are simply not five-day-a-week jobs, and partly
because some (or even many) people don't actually go straight from home to
work (or from work to home) on their surveyed day (e.g., they engage in some
trip chaining, which turns some Home-to-Work trips into HNW and NHB trips,
and turns some Work-to-Home trips into NHB and HNW trips).
Hope this helps!
sincerely,
Ken Cervenka
NCTCOG
-----Original Message-----
From: ctpp-news-bounces(a)chrispy.net
[mailto:ctpp-news-bounces@chrispy.net]On Behalf Of Jiji Kottommannil
Sent: Monday, August 16, 2004 12:09 PM
To: ctpp-news(a)chrispy.net
Subject: [CTPP] CTPP Part 3
Hi All,
I am a new user of the CTPP data and am in the process of comparing CTPP
part 3 tract-tract worker flow data to the Home-Based Work trip table
from the travel demand model I am currently working on. I came across a
few questions/issues for which I would welcome your
thoughts/experiences:
1) Do the CTPP part 3 flows account for all the home-based work trips? I
noticed that the commonly accepted home-based work attraction rate is
about 1.5 trips per total employment (NCHRP 365) and this creates more
HBW trips than there are in the CTPP part 3. Let me know if I there is
something wrong in my interpretation of the data.
2) How much success have the MPO's had in calibrating their trip
distribution models based on CTPP Part 3? What level of accuracy is
typically desired?
Thanks!
Jiji
Jiji V. Kottommannil
Transportation Modeling Specialist,E.I.T.
Crawford Bunte Brammeier
Phone: 314-878-6644, Ext. 38
Fax: 314-878-5876
_______________________________________________
ctpp-news mailing list
ctpp-news(a)chrispy.net
http://www.chrispy.net/mailman/listinfo/ctpp-news
Hi All,
I am a new user of the CTPP data and am in the process of comparing CTPP
part 3 tract-tract worker flow data to the Home-Based Work trip table
from the travel demand model I am currently working on. I came across a
few questions/issues for which I would welcome your
thoughts/experiences:
1) Do the CTPP part 3 flows account for all the home-based work trips? I
noticed that the commonly accepted home-based work attraction rate is
about 1.5 trips per total employment (NCHRP 365) and this creates more
HBW trips than there are in the CTPP part 3. Let me know if I there is
something wrong in my interpretation of the data.
2) How much success have the MPO's had in calibrating their trip
distribution models based on CTPP Part 3? What level of accuracy is
typically desired?
Thanks!
Jiji
Jiji V. Kottommannil
Transportation Modeling Specialist,E.I.T.
Crawford Bunte Brammeier
Phone: 314-878-6644, Ext. 38
Fax: 314-878-5876
All,
The CTPP Part 2 final version ASCII files have been released through the BTS Tanstats website. To download these files, please go to: http://www.transtats.bts.gov.
The CTPP 2000 Part 2 - AT PLACE OF WORK tables are organized into two distinct groups: Characteristics of All Workers and Characteristics of Workers in Households. Data documentation and SAS programs are provided in the zipped folder for each state.
Pheny Z. Smith, Ph. D.
Statistician
Office of Advance Studies
Bureau of Transportation Statistics
The note below is from Joe Salvo, who is a very active member of the Census Bureau State Data Center (SDC) network, but not a CTPP listserv member:
We have taken a close look at the counts of total workers from the 1990
and 2000 CTPP Part 2 at the Census Tract level. There seems to be an
unusual amount of volatility, with double-digit percent increases and
declines. (And, it is not a function of small bases, as many of the
tracts showing large increases/declines have several thousand workers.)
We have mapped the changes and, with the exception of two or three
areas, these "ups and downs" seem almost randomly distributed.
Has anyone else compared 1990 and 2000 CTPP data for small areas?
Joe Salvo
NYC Department of City Planning
jsalvo(a)planning.nyc.gov
Hellow to all of you,
Attached please find a copy of an "official statement" about the current status of ACS ramp-up, which I received from the Census Bureau ACS Outreach Office today. I'll update you with any new development in the future whenever I receive new information. Meanwhile, hope all of you an enjoyable and safe summer.
Sincerely,
Pheny Smith, Ph. D.
DOT FAIP Liaison
Office of Advanced Studies
Bureau of Transportation Statistics
Hi folks,
I'm a Master's student and my name is Gildemir. I'm from Brazil and I'm looking for some informations to how some tools of TransCAD works. I'm a TransCAD user for a long while and now I'm using partitioning and clustering tools to determine traffic or planning zones. So, I'm very interested to know the algorithim of this tools. I'm quite sure that somebody there could clarify me. Please let me understand how the partitioning and clustering in TranCAD works. You could send me any subjects about it? Could be papers and the own algorithm?
Sure that I'll get it as long as possible I give up of this messenge saying thanks and very glad.
Cordially,
Francisco Gildemir Ferreira da Silva
___________________________________________________________________________________
Acesse nosso portal www.click21.com.br
Porque internet grátis, nem a Embratel pode fazer mais barato. Mas pode fazer melhor.
Here are some ideas for organizing your research for the Commuting to
Downtown project. Hopefully this is not too intimidating.
****************************************************************************************************************************************************************************
Detailed Methodology / Commuting to Downtown
0. What Cities should be examined? We have 58 U.S. cities of over
300,000 population, and 68 cities of over 250,000 population. Since this
is strictly a volunteer opportunity, let's work on ANY city greater than
250,000 population. OR, any city with a downtown employment greater than
30,000 jobs. This is not intended as a hard and fast rule, just a
starting point. Hey, if someone wants to volunteer the analysis for
Toronto or Mexico City or London, heck, why not?
1. Assemble the computer files from the 1970 UTP and 1980 UTPP, if
available. These will be in the possession of the metropolitan planning
organization, the state department of transportation, or perhaps copies
were maintained by the state data center, local data centers, local
universities or local consultants. If and when you do find the 1970-1980
databases, please make sure that the FHWA has a copy for their
Journey-to-Work Data Archive (contact: Nanda Srinivasan at the FHWA).
These 1970-1980 data may be impossible to locate, or they may never have
existed, for certain cities. The Commuting to Downtown analysis for
those cities would then focus on 1990 to 2000 trends. This is the
"treasure hunt" element of this project!
2. Assemble the computer files from the 1990 CTPP and the 2000 CTPP.
The 1990 CTPP data has been widely distributed by the BTS via CD, and is
currently available on the BTS transtats site. (transtats.bts.gov). The
2000 CTPP data has been directly mailed to MPOs and State DOTs, and is
also available on the BTS transtats site.
3. Downtown definitions, Part 1. The first step may be to examine the
downtown boundaries in the 1977 Census of Retail Trade. These are the
official downtown boundaries as used in the 1980 UTPP. For the 1990
CTPP, MPOs were provided the option of re-defining their downtowns. The
"CBD of work" is a summary level in both the 1980 UTPP and the 1990 CTPP
(but not the 2000 CTPP). The analyst may find that the '77 Retail Trade
Census CBD boundaries are totally inappropriate for their cities, so the
analyst may want to draw on other resources: chambers of commerces,
"Business Improvement Districts" (BIDs); downtown development councils;
main street organizations; urban geography professors; your own
knowledge and experience. The definition of downtown, or the "central
business district" is more of a cultural and traditional notion, than a
strict definition based on employment density. The WWW is a great
resource for this sort of exercise.
4. Expanding downtowns? It will be easier for this cross-downtown
analysis to maintain a consistently-sized downtown area from past to
current census years. My recommendation is to use the best, current
definition of downtown and use those boundaries to assemble data from
the 1970, 1980 and 1990 censuses. Your own downtown may have physcially
expanded, or contracted, over the decades, but it is much harder to make
statements about increasing or decreasing employment densities when the
downtown land area is changing. As an option, you can assemble
background appendix materials on the geographic expansion/contraction of
the CBD.
5. Downtown definitions, Part 2. Be sure to develop and maintain a
correspondence file between your downtown definition and the component
geographic areas, be they census tracts, block groups, or census travel
analysis zones. Maintain these correspondence files for all census
years, given that the component geographic areas may be a different
basis (e.g., our data from the 1970 is from our old 440-zone system;
from 1980, at the block-group level; and from 1990-2000, the census zone
level.)
6. Multiple downtowns? We will want to have multiple downtowns for
certain cities including Manhattan and Chicago, perhaps San Francisco.
This would show the characteristics for the "greater downtown" compared
to the "core downtown."
7. Map of downtown. The prototype maps for downtown San Francisco,
Oakland, and San Jose are quite fuzzy. (That's my fault.) The final
product will need to be much sharper. The idea is to develop a map of
about a half-page, showing the downtown boundaries, major
transit/transportation facilities, significant landmarks (skyscrapers,
parks, city hall, etc.), scale and north arrow. We will probably want to
export any finished maps into encapsulated post-script or some other
high-resolution format. Recruit your GIS staff to prepare a map of
downtown.
8. MPO Employment data. It will be VERY useful to show the trends in
total employment in the downtown area, AND the metropolitan area, based
on the employment databases maintained by the COG/MPO. The Census
"workers-at-work" SHOULD be less than the MPO/COG estimates of "total
employment" due to multiple jobholding, weekly absenteeism, and seasonal
variation, and errors in both the CTPP and the MPO/COG total employment
estimates.
9. Commute mode shares. Data on workers working in downtown by
aggregated modes: drive alone, carpool, transit (excluding taxi), taxi
(for NYC, others), walk, bicycle, working at home. Data on workers
working in the region for transit, and total. This is used in
understanding downtown's share of regional transit commuters, and
regional total commuters. Even though our focus and interest is in
"transit commute share" the assembled data will also be useful in
understanding bicycle, walk, carpool and working-at-home shares.
10. Living downtown. Assemble data on total population and total
households. Much of the downtown literature focuses on living in
downtown, and this study can be very helpful in assembling these data.
Use standard census products like PL 94-171, SF1, or the CTPP part 1.
11. Land area. Assemble statistics on land area, in acres. This will be
useful in describing the overall worker (job) density as well as
downtown population (resident pop.) density. We will focus on gross
densities as opposed to net densities (e.g., households per residential
acres) due to the difficulty in assembling net acres (residential acres;
employment-serving acres.)
12. What's the Story? The analyst should provide some text describing
what is happening in the downtown, what are the significant events
including transit system openings and changes in major buildings. What
are the hopes and aspirations for the downtown in your community?
******************************************************************************************************************************************************************
**************************************************************
Charles L. Purvis, AICP
Principal Transportation Planner/Analyst
Metropolitan Transportation Commission
101 Eighth Street
Oakland, CA 94607-4700
(510) 464-7731 (office)
(510) 464-7848 (fax)
www: http://www.mtc.ca.gov/
Census WWW: http://www.bayareacensus.ca.gov/
**************************************************************
Our TRB Urban Data Committee is still working on the "Commuting to
Downtown" study. The goal is to produce a time-series database on
commute mode shares, employment, employment density, population trends,
and overall development trends in downtown areas of large cities
(300,000+ population) in the United States. Data from the 1970 through
2000 decennial censuses can be used in developing this database, though
data from the 1970, perhaps even the 1980 Census, may be hard to come
by.
The Committee is planning a conference session for the January 2005
annual meeting of the Transportation Research Board in Washington, DC.
I'm envisioning a small panel of 3-to-5 committee members and study
contributors to present results for the various downtown databases that
have been assembled.
The project is described on the RECENTLY UPDATED urban data committee
web page, at: http://www.mtc.ca.gov/trb/urban/ . We now have prototype
maps and analyses for the three large cities in the San Francisco Bay
Area, and Philadelphia. The Philadelphia Story is interesting in showing
the trends in downtown population, as well as downtown employment. Both
subjects (population & employment trends) are of interest.
In terms of format for these initial analyses, PDF format appears to be
the most efficient, though spreadsheets, word documents, etc., are OK.
We're really interested in large cities with population greater than
300,000. If you're lucky enough to be the MPO with any of these large
cities, please feel free to volunteer! Drop me an e-mail. (Also, several
folk have been interested in working on the New York downtown analysis.
Please contact Kuo-Ann Chiao of NYMTC, *especially* if you have access
to the pre-2000 Census data....)
To help things along with the 1980 UTPP, we have extracted the 1980
UTPP, Part 3, Table 5 data, at tract-of-work or zone-of-work for
available regions, including: New York, Boston, Delaware State, Kansas
City, St. Louis, St. Paul, Atlanta, Cleveland, Cincinnati, Toledo,
Seattle, and Chicago. (These extracts are based on the original 1980
UTPP datafiles provided by the State DOTs and MPOs that are archived by
USDOT, and MTC's new SAS code.) The data file is
here:http://www.mtc.ca.gov/trb/urban/commute/ filename:
tab305_extract.zip. If you need help in analyzing your original data
files, please contact me or Nanda Srinivasan at FHWA.
E-mail me (not the CTPP-News listserv) at: cpurvis at mtc.ca.gov
You may also be interest in the HOUSEHOLD TRAVEL SURVEYS ON THE WWW
project sponsored by the urban data committee, at:
http://www.mtc.ca.gov/trb/urban/hhsurvey.html
cheers,
Chuck Purvis, MTC
**************************************************************
Charles L. Purvis, AICP
Principal Transportation Planner/Analyst
Metropolitan Transportation Commission
101 Eighth Street
Oakland, CA 94607-4700
(510) 464-7731 (office)
(510) 464-7848 (fax)
www: http://www.mtc.ca.gov/
Census WWW: http://www.bayareacensus.ca.gov/
**************************************************************
Jiji:
The 97,526 count of employed persons is for Sangamon
County-of-Residence. I checked this on the Census Bureau's Demographic
Profile site, and this 97,526 figure is correct. This is definitely
"residence-end" information, not the "work-end". Information on employed
residents (employed labor force) is available from SF3, SF4, PUMS and
the CTPP Part 1.
http://censtats.census.gov/pub/Profiles.shtml
The CTPP Part 2 count of workers is for Sangamon County as the
county-of-work. Think of this as workers at county-of-work. Total
employment, or "jobs", should be a tad higher due to moonlighting and
weekly absenteeism. Neither the CTPP nor the standard Census products
include the secondary, or moonlighting job held by an employed worker.
Do note that the CTPP data *is* from the decennial census long form; it
(the CTPP) is just not a standard product.
CTPP Part 1 is very similar to the standard Census products in that the
data is reported by the area-of-residence.
cheers,
Chuck Purvis, MTC
>>> "Jiji Kottommannil" <jkottommannil(a)cbbtraffic.com> 07/07/04 01:20PM
>>>
Hi All,
I compared the employment numbers from Census 2000 and CTPP 2000 part
2
for Sangamon County, Illinois and found what looked like an
inconsistency.
According to Census 2000, the county had 97,526 employed persons,
whereas according to CTPP 2000 Part 2, the county had 112,023 workers.
I assumed that since these are from the same source, both take care of
the second job and absenteeism factors. Or does CTPP count second jobs
too?
Is the cause of the difference then due to the fact that the Census
number accounts for only those who live in that county whereas CTPP
counts all workers including those who come to work from other
counties?
Has anyone had a similar experience with CTPP 2000 Part 2 data?
Any input on this issue would be greatly appreciated.
********************************************************************************************************
Census data is place of residence while the CTPP Part 2 data is place of
work.
>>> "Jiji Kottommannil" <jkottommannil(a)CBBTRAFFIC.COM> 7/7/04 3:20:30
PM >>>
Hi All,
I compared the employment numbers from Census 2000 and CTPP 2000 part
2
for Sangamon County, Illinois and found what looked like an
inconsistency.
According to Census 2000, the county had 97,526 employed persons,
whereas according to CTPP 2000 Part 2, the county had 112,023 workers.
I assumed that since these are from the same source, both take care of
the second job and absenteeism factors. Or does CTPP count second jobs
too?
Is the cause of the difference then due to the fact that the Census
number accounts for only those who live in that county whereas CTPP
counts all workers including those who come to work from other
counties?
Has anyone had a similar experience with CTPP 2000 Part 2 data?
Any input on this issue would be greatly appreciated.
Thanks!
Jiji
Jiji V. Kottommannil
Transportation Modeling Specialist,E.I.T.
Crawford Bunte Brammeier
Phone: 314-878-6644, Ext. 38
Fax: 314-878-5876
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