RE: [CTPP] TAZ Development

Well, I've received a few responses to my plea for direction, and I thank those who responded thus far. Jonathan Lupton is correct, if anyone seems to have a reasonable handle on this issue, please "chime in". We don't want to leave him holding the bag with his "pedestrian knowledge" as the epitome of the state of travel demand! ;-) What I have developed to date is a TAZ system that should reasonable provide us with enough detail to get a better handle on forecasted volumes on the region's "minor arterial" network. In the past the focus had been primarily on the "principal arterials". In the next phase of this TAZ development, I plan to aggregate this system into a nested system that could be used as a "fall-back" in case the more detailed one resulted in large numbers of empty cells when sent to the Census Bureau. This is where I find myself at the moment. How many of the smaller TAZs do I need to combine? Frank, your notes indicated 240 households or about 600 people. I looked at that and found 39 percent of my TAZs fall below that number when I "populate" the cells with year-2000 Census data. Jonathan suggested 1000 population or employment. Again, looking at my TAZs, I find 56 percent of them fall below THAT number. Fortunately (I think), the problem TAZs are found overwhelmingly in the rural or developing areas of our region OR they are TAZs in which I have large employment concentrations. Given that scenario, I am attempting to aggregate these TAZs into something larger. The question is, what should my minimum be? Patricia, I agree with your thoughts on the use of ACS data. However, in this instance, my concern is with the upcoming 2010 census and the information we hope to obtain from a CTPP-like product that has been urged by AASHTO and its Standing Committee on Planning. Having dealt with CTPP (or UTPP) tabulations for several decades, this new realm of ACS and LEHD apparently will be the way to go, but I am still hoping that something will come out of the 2010 census that will reasonably approximate that older product. Thanks so far for the comments. I hope they continue as we head into the decennial census year. ________________________________ From: ctpp-news-bounces(a)chrispy.net [mailto:ctpp-news-bounces@chrispy.net] On Behalf Of Jonathan Lupton Sent: Tuesday, August 04, 2009 4:32 PM To: ctpp-news(a)chrispy.net Subject: RE: [CTPP] TAZ Development Mr. Paddock: I bounced this same question off Nanda Srinivasan years ago (ca. 2006) back when he was involved in the CTPP. He seemed to have as firm a grip on this kind of issue as anybody. I remember being told that the minimum TAZ size should be about 1,000 population or 1,000 employment, to avoid disclosure problems. I do not know what would happen in a TAZ that met one of these thresholds but not the other. I am not offering the information above as anything definitive; as best I remember there seemed to be a lot of deliberate vagueness about appropriate TAZ size. I know our TAZ's in my region are presently quite a bit smaller than these thresholds in most cases. I would dare to predict that LED may end up replacing CTPP in practical terms. At its "On the Map" web site, LED already provides TAZ-level employment by detailed industry for much of the country, including my region. LED doesn't seem to have a disclosure problem, although I think it doesn't yet provide the depth of journey to work data as in pt. 3 of the CTPP. If anybody knows more, please, please chime in. I'd hate to think that the pedestrian knowledge of a peon like me represents the best information among the Great Minds of transportation modeling. Jonathan Lupton AICP Research Planner Metroplan Little Rock AR From: ctpp-news-bounces(a)chrispy.net [mailto:ctpp-news-bounces@chrispy.net] On Behalf Of Paddock, Bob Sent: Tuesday, August 04, 2009 3:33 PM To: 'ctpp-news(a)chrispy.net' Subject: [CTPP] TAZ Development I must admit that, of late, I have gotten lost in the woods while trying to see all the trees. During these past months I have been engaged in developing a new TAZ system for the Minneapolis - St. Paul MPO area that will both serve the needs of travel demand modeling here at the Metropolitan Council AND provide us with the information we want from a 2010 CTPP-like product. This new TAZ system is substantially more refined than those of the past and should result in reasonable travel loadings on our arterial roadway network. However, certain issues have been raising their knobby heads regarding zone size that probably will clash with Census Disclosure Board rules. Does anyone have a reasonable idea as to what minimum population or household levels a TAZ will need to attain in order to circumvent large numbers of "blank" cells? I suspect that there is not an easy, uncomplicated answer but would like to hear one nonetheless. Bob Paddock Transportation Planning Metropolitan Council Bob.paddock(a)metc.state.mn.us 651 / 602-1340