RE: [CTPP] re: Statewide TAZes - ctpp-news

29 Sep 1999

Mr. Herrick; 
The 1990 statewide CTPP used county and cities over 2,500 for place of work,
and also township level for place of residence coding.  I imagine that's
what you'll get in 2000 if you do nothing at this point, but perhaps the
Census people on this list can correct me.  If you are going to do statewide
modeling, what you should do is the same thing any urban MPO staff should do
- first determine what network you want to model and then partition your
state into zones based on access to this network.  My guess is that city to
city would not be good enough for you, except for the smallest of towns.
Even what Mr. Purvis describes is more convenience than criteria, but as he
notes there's not much time left.  If you don't have the time, then look at
what you'd like to model for one typical rural county in Kansas and figure
out which level of existing Census geography seems to best match the access
pattern, then ask for that level as the TAZ level.

Sam Granato

...
  -----Original Message-----
 From:	Chuck Purvis (MTC) [SMTP:cpurvis@mtc.ca.gov]
 Sent:	Wednesday, September 29, 1999 11:25 AM
 To:	Chris Herrick; ctpp-news(a)chrispy.net
 Subject:	[CTPP] re: Statewide TAZes

 Chris:

 I believe that Caltrans (California Department of Transportation)
 will be building any new statewide travel analysis zones on
 MPO-defined zones in our metropolitan areas; and census tracts in
 non-metropolitan areas. This should be adequate for purposes of
 developing a statewide TAZ system. <The 4,000 census zones I've 
 defined in my region of 6.8 million people, will probably be 
 collapsed to about 300 statewide TAZes by Caltrans.>

 On the other hand, it may prove useful to request block group level
 TAZes in non-metro counties. If I were the county planner in Lake
 County (the non-metro county just north of my Napa County in Calif.)
 I would much prefer to get CTPP data at the block group level than
 tract level (this assumes the absence of TAZes for non-metro 
 counties!)

 I would hope that the default option for Statewide TAZes are 
 finer-grained than counties!! That doesn't make sense to me.

 My recommendation would be to monitor the TAZ development in your 
 MPOs; then tally up the number of census tracts and block groups in 
 each of your counties. Depending on the level of detail, and the 
 needs of your local non-metro county planners, decide on either 
 tracts or block groups. Either that, or define TAZes on a 
 block-by-block basis for your entire state. That sounds like a six 
 person month effort to be completed in 30 days from today....

 I'm uncertain about the rules established by the Census Bureau, but I 
 believe they're only going to allow one set of TAZes for each county. 
 So, in metropolitan counties, it's apparently up to the MPO and State 
 DOT to negotiate the finest-grained system that meets or exceeds the 
 needs of both <I should be corrected if I'm wrong.>

 cheers,

  Chuck Purvis, MTC

  What are other states doing with updating their
TAZs in preparation
 for the 2000 census?  It is my understanding that if a state does
 not submit a TAZ update the counties will be used as TAZs for CTPP
 purposes.  

 The type of data we would be interested in at this point would be
 journey to work trips for county to county, city to city, and city
 to county.  We do not currently have a statewide model but are
 interested in possible looking into the benefits of building one. 
 Please inform me on what direction we should take.

                                        Chris Herrick, P.E.
                                        Statewide Planning Engineer
                                        Kansas Department of
                                        Transportation
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 Chuck Purvis, AICP
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 Metropolitan Transportation Commission
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