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@chrispy.net [mailto:ctpp-news-bounces@chrispy.net] On Behalf Of Paddock, Bob
Sent: Tuesday, August 04, 2009 3:33 PM
To: 'ctpp-news@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@metc.state.mn.us

651 / 602-1340