[CTPP] Commuter Flow Data Concerns

A few of us have been getting calls and emails from people who have been looking at the commuter follow data the Census Bureau just released, the On the Map (LEHD) and some of the earlier flow data. If you have, you probably noticed some interesting (or maybe wierd) things. Needless to say a good understanding of the data is needed to sort out some of the issues. Below are some references and points that may be of interest. What are people noticing with the data? --------------- In the January 20011 Status Report newsletter there is an article from the NY State DOT by the late Nathan Erlbaum which discusses the issues surrounding the various flow data sets. The article “Commutation Flow: CTPP 2000, ACS and CTPP, and LEHD-OTM” can be found at http://www.trbcensus.com/newsltr/sr0111.pdf (starting on page 6). In it is a link to a larger body of work that Nathan did on the topic. a read of this is must if you are having questions about the data. Regarding the LEHD and CTPP flow data, there is an NCHRP report that has been completed that is also worth reviewing. It gets into detail about some of the differences between the two data sets. It can be found at http://onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP08-36%2898%29_FR.pdf Elaine Murakami reminds me that 1. LEHD does not include self-employed (approx. 10%) 2. LEHD only recently included federal workers, but does not include MILITARY 3. LEHD is jobs and ACS is "workers at work". Periodically issue like this pop up and there is a discussion on the list serve. there is an archive but off course it takes some time to mine and search through. If anyone is interested in looking through it, it is open to the public and available at http://www.chrispy.net/pipermail/ctpp-news/. There was a discussion around august of 2010 dealing with flow data but it centered more on availability. Hope this helps. -- Ed Christopher 708-283-3534 (V) 708-574-8131 (cell) FHWA RC-TST-PLN 4749 Lincoln Mall Drive, Suite 600 Matteson, IL 60443