RE: [CTPP] Release of CTPP Part 3 Flat ASCII files

hmmm...thanks for the reminder, Chuck: The person living in Alaska but working in Dallas during the "reference week" might be noting: -- 20 minutes as his/her trip from the "regular" home in Alaska to the "regular" workplace in Alaska. -- 20 minutes as his/her trip from the "reference week" home in Dallas to the "reference week" workplace in Dallas. Either way, it seems that such a trip (as well as others that fit some category of strangeness) should simply be dropped from most journey-to-work regional analysis. Which brings up a subsequent question: Should a Planner simply drop those kinds of trips from a travel pattern analysis, or perhaps "expand" the remaining zone-to-zone trips in such a way that the original Census-estimated number of workers in the "place of work" zone is still preserved? The good news is that the percentage of zone-to-zone trips that fit this strange category of a temporary "reference week" workplace that requires a different temporary "reference week" home place is not very large. Ken C. -----Original Message----- From: Chuck Purvis [mailto:CPurvis@mtc.ca.gov] Sent: Friday, May 21, 2004 10:42 AM To: ctpp-news(a)chrispy.net Subject: Re: [CTPP] Release of CTPP Part 3 Flat ASCII files Hey Ken: The ultra-long distance commuters I just throw away. I put them in the same bucket as the weekly absentees. Or, it may help to try to sort the commute data into: commutes from home-to-work; and, commutes from "not home"-to-work. (Note that the census doesn't ask where you started your commute, it asks: "at what location did this person work last week?" Though the question on commute time departure *does* ask: "What time did this person usually leave home to go to work last week?") For interregional commuters, I use my common sense and select the counties neighboring my region that have legitimate opportunities for daily commute trips. Perhaps this is a three-hour maximum from the edge of the region? Counties in California are fairly large, so I use just 12 neighbor counties surrounding the SF Bay Area. Texas has MANY smaller-sized counties, so I imagine you would have an inner ring and outer ring(s) of surrounding / neighboring counties. Then, if you have time, you can build some tract-to-tract desire lines (with distance) to calculate the tract-to-tract distances, reported average commute duration, and derived commute speed, to determine if the interregional commutes are sensible or silly. I don't know what I would do with a seemingly reasonable interregional commute value that has a unreasonable travel time - - perhaps the travel time is mis-coded, or perhaps this is another case where the worker is NOT starting their commute from THEIR home!? I would probably accept the numbers of commuters value, but blank out the commute time as a missing value. Another idea is to use the statewide travel model system to build a statewide zone-to-zone commuter matrix, then develop commute length (distance) frequency distributions to isolate the ultra-long, intra-state commutes, their reported commute durations, and the derived commute speeds. That would be preferable to a crow-flow distance desire line analysis. (By the way, I haven't tested any of these methods. They're just some ideas to share.) Chuck Purvis, MTC This question has probably been asked before, but I don't recall the answer... What sort of adjustments do people make with CTPP data, to deal with the extreme "long-distance" commuters that are actually just "temporarily re-assigned" workers? This is not an error in the CTPP collection or summary process, but rather a result of the way the long form questions were answered. For example, here is a record that got "expanded" to four people: -- The Place of Residence is a County in Alaska -- The Place of Work is a County in Texas (Dallas) -- The commute time is 20 minutes What this is saying is that the person isn't really commuting each day from their home in Alaska, but is instead commuting to a place in Dallas County from some temporary residence (a hotel, perhaps) within the Dallas-Fort Worth area. Such an extreme example is easy to recognize, but what about other examples which fall into the "not sure" category when it comes to whether a person's normal place of residence is really the point where they are truly starting their commute trip? Perhaps a very high "average speed" based on "travel time" and "straight-line distance" could be used to flag such records? Ken Cervenka North Central Texas COG