[CTPP] Income variable in future CTPP-like products

Despite the uncertainty of 2006 American Community Survey (ACS) budgeting and implementation, I am raising this query on future CTPP-like products using ACS. For the CTPP2000, there were 2 FLOW (part 3) tables using income: Table 3-5 Income (8 classes + total) Table 3-7 Income (4 classes +total ) by Means of Transportation (4 classes + total) Both of these tables were subject to the Census Bureau's Disclosure Review Board (DRB) requirement of 3 unweighted records, resulting in very high suppression of Origin/Destination pairs at the tract-to-tract (about 70 percent), and TAZ-to-TAZ (often over 80 percent) level. Because the sample size in ACS (even after 5 years of data accumulation) are expected to be perhaps 40-60 percent that of the 2000 decennial census long form sample, it will be even more difficult to reach the threshold of 3 unweighted records for flow tabulation. The CB's DRB has told us that for special tabulations (like the CTPP) "rounding and thresholds are here to stay." Right now, the next level of geography is Place (city or town), which is often too large to be meaningful. We understand that the CB plans to use PUMA as a standard tabulation unit, which could result in a very useful PUMA-to-PUMA flow table for large metropolitan areas, but since PUMAs require 100,000 population, this would be not very useful for smaller metropolitan areas. Here are some alternatives to consider: 1. Using MEDIAN INCOME instead of a distribution. At least one person at the CB thinks that the DRB would be less concerned about this. While this might work for Table 3-5, I don't think it would work for Table 3-7, because there would be a significant probability for one record for a particular mode, e.g. transit, so that the median would be the same as the individual record. 2. Having a SuperTAZ or SuperTract new geographic unit for flow tabulations that include an income variable. How big would a SuperTAZ or SuperTract need to be? I don't know, but my guess is that it would need to be on the order of 4-5 census tracts combined. We know that if we combine only 2 tracts, it will result in approximately 70 percent of suppression, because the unweighted records would be similar in number to the CTPP 2000 tract-to-tract numbers. 3. Omit the income tables from an ACS Flow tabulation, and find another data source. Please let me know what you think, and especially if you have ideas for alternatives. AASHTO SCOP has convened a Census Data Working Group. It is chaired by Jonette Kreideweis of MN DOT. Information about this group was included in the August 2005 CTPP Status Report http://www.fhwa.dot.gov/ctpp/sr0805.htm. AMPO and APTA have now been included as members. Elaine Murakami FHWA Office of Planning 206-220-4460 (Seattle)