12 Jun
2008
12 Jun
'08
4:49 p.m.
I'll throw my 2 cents in since there is no "hard and fast" rule for how
small your TAZs for census data should be. Elaine is right that we have
heard that the CB would prefer something in the neighborhood of 1,200.
In fact we can find folks at the Census that would say even 1,200 is too
small given confidentiality and data quality rules. The 1,200 actually
comes from the minimum size that a census tract can be
(http://www.census.gov/geo/www/psap2010/tract_criteria.pdf). However,
1,000 or even smaller comes from our desire in the transportation
business to have the smallest sized zones as possible. Since we have
not "hit the wall" yet on the what the final TAZ sizes can be I still
tell people that the smallest TAZs will be the size that we have all
grown up with and learned to love. That's the plan and goal. Keep them
as small as possible. Complicating all of this are the disclosure rules
that the Census Bureau is arbitrarily putting on our transportation data
request. And yes, I meant to say arbitrary which is exactly what is
happening and is part of the basis of the AASHTO appeal to the DRB on
behalf of the CTPP community.
Incidentally, the minimum population size of a block group zone will be
600 people (http://www.census.gov/geo/www/psap2010/bg_criteria.pdf) but
there are no assurances as to what data will actually be release at the
block group level. Given the way the disclosure rules are shaping up
and the statistical collapsing schema currently inplay one could
legitimately wonder what block group data we will actually see.
As far as adding workers and residents together when considering zone
sizes we have never been able to get that concept in play. Another
concept that has not caught on is having different zones system for
resident data tables than work place data tables...
Jonathan Lupton wrote:
Ms. Murakami just mentioned the TAZ population thresholds, which got
me thinking.
My MPO (Metroplan in Little Rock) just had a meeting yesterday in
which the subject of TAZs for the approaching 2010 CTPP came up. I
told the group that, to the best of my memory (based on a conversation
with Nanda Srinivasan a couple of years ago), a TAZ for future CTPPs
could have a minimum of 1,000, either in total population OR total
employment. Your statement that the preferred population for a TAZ
should be "at least 1,200" partially contradicted this. But I may have
remembered wrongly. Could you please clarify what a good standard
would be for TAZ's? Can employment be used as a minimum instead? Would
anyone else like to comment on TAZ sizes?
Jonathan Lupton
Metroplan
501-372-3300
Murakami, Elaine wrote:
--
Ed Christopher
708-283-3534 (V)
708-574-8131 (cell)
FHWA RC-TST-PLN
19900 Governors Dr
Olympia Fields, IL 60461
We are planning to have 5-year ACS data
accumulated for small area
tabulation. "Small area" means census tracts, or TAZs, as defined
by
MPOs. We are planning that this would be 2006 thru 2010 ACS data,
so
that 2010 Census geography and sample weighting adjustments can be
incorporated. This data would be available approximately 2012.
To summarize:
Base TAZs (Census would prefer at least 1,200 population)
Medium TAZs -- at least 20,000 population
Large TAZs -- at least 65,000 population
The Medium and Large TAZs would be used for annual and 3-year ACS
tabulations. The Base TAZs require 5 years of ACS data.
Elaine Murakami
FHWA Office of Planning
206-220-4460
-----Original Message-----
From: ctpp-news-bounces(a)chrispy.net
[mailto:ctpp-news-bounces@chrispy.net] On Behalf Of Bill Moore
Sent: Thursday, June 12, 2008 11:21 AM
To: 'ctpp-news(a)chrispy.net'
Subject: RE: [CTPP] CTPP Update
Ed:
---------------------------------------------------------------
_______________________________________________
ctpp-news mailing list
ctpp-news(a)chrispy.net
http://www.chrispy.net/mailman/listinfo/ctpp-news From a small (~135,000 pop) MPO perspective, the
implications of
these
super-TAZs for travel demand modeling are devastating. If 65K, we
would
have two TAZs; if 20K, we would have six or seven. Fortunately, we
are
also an attainment area and are not mandated to do modeling at all;
however a new TMA with population of 200,000 would be so mandated
and
would have a total of three or 10, respectively, so it would become
virtually impossible to do modeling for AQ conformity.
The four MPOs (howdy, Larry) along the Front Range are trying to
develop
an integrated model for a population of ~3.5 million, so at 65K
would
have only 54 TAZs, or at 20K only 175. The latter number is far
less
than we now have (306) in the Pueblo MPO - the smallest of the four.
Bill Moore, MPO Administrator
PACOG MPO/TPR
-----Original Message-----
From: ctpp-news-bounces(a)chrispy.net
[mailto:ctpp-news-bounces@chrispy.net]On Behalf Of Ed Christopher
Sent: Wednesday, June 11, 2008 3:33 PM
To: ctpp-news(a)chrispy.net
Subject: Re: [CTPP] CTPP Update
Larry--Yes, when we creat 20,000 and 65,000 TAZs our goal is to get
tablulations for these areas. Or course the DRB would have to
approve
any tables. The current problem with the ACS 1 and 3-year data (due
out
at the end of the year) that the Census releases is that your data
coverage in like swiss cheese. You get data for some areas and not
others. Our plan is to have complete coverage to eliminate this
problem
with any tables paid for with CTPP dollars. Who knows maybe we can
get
the Census Bureau to see the light and adopt the concept of having
zonal
coverage consistent with the data release thresholds for their data
products as well.
Larry Mugler wrote:
If we create "super" tazs with
populations of 20,000 and/or
65,000,
would we be able to get tabulations for such areas?
Larry G. Mugler, AICP - Planning Services Manager
303-480-6759 - Customer Resource and Support
Denver Regional Council of Governments
-----Original Message-----
From: ctpp-news-bounces(a)chrispy.net
[mailto:ctpp-news-bounces@chrispy.net] On Behalf Of Murakami,
Elaine
Sent: Wednesday, June 11, 2008 12:43 PM
To: ctpp-news(a)chrispy.net
Subject: RE: [CTPP] CTPP Update
Re: poverty and Income comparisons between Census 2000 Long Form
and
ACS:
The only report I am familiar with is:
http://www.census.gov/acs/www/Downloads/Report05.pdf
Pages 34-37 discuss county-level comparisons. These are
comparisons
between the Census 2000 Long Form (aka sample) and the ACS "C2SS",
and
18 of the test ACS counties. They found that the C2SS results
consistently had lower incomes than the Census 2000 sample, and
therefore, a higher poverty ratio. They found that income
allocation
occurs 30 percent in the Census 2000 sample, and 24% in the C2SS.
I do not know if the Census Bureau has pursued other research on
how
ACS
respondents answer the income questions.
Elaine
-----Original Message-----
From: ctpp-news-bounces(a)chrispy.net
[mailto:ctpp-news-bounces@chrispy.net] On Behalf Of Ed Christopher
Sent: Wednesday, June 11, 2008 9:50 AM
To: ctpp-news maillist
Subject: [CTPP] CTPP Update
On May 21 and June 4 members of the CTPP team conducted a series
of
webinars to help bring our community up-to-speed on several of the
CTPP
activities. The slides from these presentations
can be downloaded
from
our webinar room at http://fhwa.acrobat.com/ctpp1
(enter as a
guest)
and
the responses to many of the questions asked
during the meetings
are
presented below. If folks have additional questions please feel
free
to
post them to the list serve and someone on the
CTPP team will
attempt
to
answer them.
CTPP Webinar - Questions and Answers
Question: Will the 3-year CTPP data product based on ACS include
tables
by race and household income?
Response: Yes but the best source for information on race will
still
be
the Census Bureau's standard ACS tabulations
found on American
FactFinder (http://factfinder.census.gov/). The 3-year CTPP
proposed
tables for parts 1 and 2 include a few tables with the variable
"minority status." Also, there are various tables with the
variables -
Income, Poverty Status and Worker Earnings that will be available.
Please note that Poverty Status is a calculated variable based on
household income, family size, number of children and number of
family
members over the age of 65.
Question: Since the new CTPP products will be based on data
collected
over 3 years (or 5 years), to which year will the income be
adjusted?
Response: Income will be adjusted to the last year of the survey
period. For the first 3-year product all incomes will adjusted
to
2007.
Question: Is there data available on zero car households? If yes,
what
geography level is it available?
Response: Yes, there will be information available for zero car
households in both the 3-year CTPP data product and as part of the
standard Census products. The data will be available for
geographic
areas greater than 20,000 residents.
Question: Slides 6 & 7 of the DRB presentation show different
percentages of data lost due to DRB rules, why is that?
Response: Slide 6 showed the number of workers lost while slide 7
showed the number of origin-destination pairs lost. The point is
that
when thresholds were applied to CTPP Part 3 data as was the case
with
the 2000 data, many folks looked at the loss of workers as being
significant but more surprising was actual loss of individual O-D
pairs. All in all table thresholds devastated the part 3 flow
data.
Question: 2005 ACS data doesn't have information on Group
Quarters,
but
the 2006 and 2007 do. How is this being handled
in the 3-year
2007
ACS
products?
Response: The Group Quarter data available for 2 years (2006 and
2007)
will be reweighed to account for the missing
year.
Question: Will the variable - Means of Transportation to Work have
walk
and bike modes combined? Also, what about taxi,
bus and other?
Response: Regarding the 3-year CTPP data product there are
multiple
category lists for the variable - Means of Transportation to Work.
There are a few tables all 17 modes plus the total are shown
separately
but then there are many others where walk and
bike have been
collapsed
together. A great deal of the detail on the mode variable is in
the
hands of the Census Bureau's disclosure Review Board. Currently
they
have proposed some very tight restrictions on the proposed 3-year
CTPP
tables. Please see http://trbcensus.com/drb/ for more
Question: Do you have anything on the TAZ definition timeframe
that
you
can share with the group?
Response: Please see our Status Report newsletter for the latest
http://www.TRBcensus.com/newsltr/sr052008.pdf.
Question: Can you talk about the difference in income between ACS
and
Long Form?
Response: In Census 2000, the question was asked during April for
the
previous year, 1999. Because April is so close to IRS annual
return
data it was felt that "good" income data was being collected
because
it
was fresh in people's minds. However, for
the ACS the same
questions
are asked, but the respondent could be getting the survey during
any
month of year (depending on when she/he received the form). This
reported income is then adjusted to the current year (year of
tabulation) based on CPI. There are several issues with this with
the
largest being that at anytime during the year most people do not
how
much money they made in the last 12 months. Needless to say the
income
question is messy.
Question: Poverty rates seem discontinuous, higher. Any ideas why?
Response: Yes, they are discontinuous. Hopefully they will look
better
with the 3-year ACS data products.
Question: If the DRB is so strict with its rules then why bother
with
new TAZs?
Response: We hope that the DRB will relax its rules but having
TAZs
that correspond to the ACS data release products (65,000 pop TAZs,
20,000 pop TAZs and small TAZs) will help us in the future all
sorts
of
data products. Having geography match the data
release seems to
make
good sense so that we can at least get complete coverage
(wall-to-wall)
within a region.
Question: What are the implications of rising fuel prices on
travel
choices on mode to work? Has anybody thought about it, especially
with
aggregating 3 years worth of data? Since the ACS
asks about
"usual"
mode, it could still miss modes used only part of the time.
Response: The 3 year ACS trend data might look a lot different
than
the
2000 data. This might be a good research
question.
Question: Is the category list for the variable - occupation being
consolidated?
Response: No, DRB has not asked us to collapse the variables -
industry
or occupation.
Question: Is anybody planning to write to Congress about the DRB
issue?
Response: AASHTO SCOP is sending a letter to the
Census Bureau to
appeal
the DRB decision. As FHWA staff, we cannot
contact Congress
directly
but we know that many regional agencies do talk with their
Congressional
delegations. It is somewhat ironic but many of
the
congressionally
mandated analysis like the FTA New Starts program and
environmental
justice analysis all need data at a smaller geography level which
will
be difficult to obtain with the DRB's current rules.
Question: We are relatively a new MPO and I have a CTPP 101
question.
As an MPO do we need to provide you any information, and what are
our
sources of information regarding CTPP specifically regarding TAZs?
Response: The CTPP listserve is a good place for information
regarding
ongoing CTPP related activities. The TAZ definition process is
planned
for March/April of 2009 and it is recommended that MPO's allocate
some
budget when preparing their work plans for FY 2009, especially for
new
MPOs. The CTPP Status Report is also a good source of information.
If
you have any particular questions please do not hesitate to
contact
anyone one of us on the CTPP team.
Question: Somewhere it was noted the first CTPP ACS product would
be
available in 2009 for areas of 20,000 or more for places and
counties.
Response: Yes that is correct. We are still in the negotiation
stage
regarding some DRB issues but this is our GOAL. This first CTPP
product
would use 3 years of ACS
data.
Question: There was also a mention of TAZ level data also for
20,000
population threshold. However, I am not sure if this is included
in
the
first 3 year product for 2009, or whether the
first TAZ level
report
will not be available until 2012 with a 5 year product.
Response: To get "small" area geography like a TAZ or a census
tract,
the census requires 5 years of ACS data. So, we are planning to
wait
for
2006 thru 2010 ACS data to incorporate 2010
Census geography and
weights, which we hope would be tabulated by 2012. This will
likely
require some data synthesis before release. Because of the
probability
that the data will be synthetic, we do not
anticipate any
population
threshold.
--
Ed Christopher
Resource Center Planning Team
Federal Highway Administration
19900 Governors Drive
Olympia Fields, Illinois 60461
708-283-3534 (V) 708-574-8131 (cell)
708-283-3501 (F)
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--
Ed Christopher
Resource Center Planning Team
Federal Highway Administration
19900 Governors Drive
Olympia Fields, Illinois 60461
708-283-3534 (V) 708-574-8131 (cell)
708-283-3501 (F)
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