Re: [CTPP] TAZs and BBSP (Block Boundary Suggestion Program)

OKI This and several other comments I've been reading from MPO staffs in the past several weeks have left me a bit baffled. I offer the following comments in the hope that they'll be helpful to some of the agencies on this e-mail list that are about to review their traffic zone geography. 1) The only valid criteria for traffic zone delineation is access patterns to the transportation network being modeled. Census geography is a constraint, not a criteria. Assuming that you have a reasonably detailed network to model, you'll need in some areas some pretty small zones, geographically speaking. (If this leads to zones with populations so small that the Census is not comfortable reporting data for confidentiality reasons, we can work around that-we just need to know where that level is.) 2) Historical continuity? That's what census tracts are for. And without quoting Henry Ford, in a country where people move on average every 5 years, history won't count for much in an area as small as a TAZ. 3) Statistical confidence (in data from very small areas)? I assume we've all had our Stats 101 and know what we're getting into with small sample populations (to say nothing of non-response and mis-response). But by going with smaller zones, your erosion of statistical confidence is more than made up for, in my view, by more accurate coding of network access. Feel free to contact with any questions or comments. Sam Granato, Cedar Rapids MPO