Thanks for the shout out, Don! I did post this as a comment on TMIP:
Just a note: in my experience home-based work is seldom the vast majority of morning peak
travel: nation-wide it is about 40 percent of vehicle trips in the morning peak, when
looking at metro level it can rise to 60 percent or so. Of course the evening peak is
even less likely to have home-based work travel.
In the 2009 NHTS, just under 20 percent of workers stopped for one or more reasons in the
morning before going to work--a stop of 30 minutes or more. This estimate was much higher
for women and people with children in the household. The percent of workers stopping
during the commute is similar to the estimate in 2001, so while the percent of stops
during the commute may not be growing it remains substantial. These are often
'pick-up/drop-off' trips, and it may pay to look at the passenger's purpose to
understand what kind of trip (school, other workers, etc.)
It is the case perhaps that the non-work travel vehicle travel occurs on arterial more
than highways, and may be spread out rather than in the most congested corridors. But
for overall vehicle travel estimation and flows we should keep in mind the impact of
these non-work trips and stops. Nancy McGuckin
Travel Behavior Analyst
On Friday, August 12, 2016 10:00 AM, "ctpp-news-request(a)chrispy.net"
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1. CTPP Flows and Traffic Assignments (Cervenka, Kenneth (FTA))
2. Re: CTPP Flows and Traffic Assignments (Don Cooper)
Date: Fri, 12 Aug 2016 12:09:18 +0000
From: "Cervenka, Kenneth (FTA)" <Kenneth.Cervenka(a)dot.gov>
Subject: [CTPP] CTPP Flows and Traffic Assignments
To: "ctpp-news(a)chrispy.net" <ctpp-news(a)chrispy.net>
Content-Type: text/plain; charset="us-ascii"
I sent the following to the TMIP (Travel Model Improvement Program) listserv earlier this
morning, but since this is focused on CTPP, I would be happy to get comments from the CTPP
group as well.
It is somewhat common practice to compare district-to-district flows consisting of
aggregations of TAZ-to-TAZ travel model outputs for Home-to-Work person trips to similar
home-to-work aggregations based on CTPP flows. Since most AM peak period auto travel
consists of home-to-work movements, what successes or failures have forecasters had in the
use of TAZ-to-TAZ CTPP data in an AM peak period UE traffic assignment? Or some variation
that might include enhancements to the commuter flow data to represent the (relatively
small) non-commuter AM Peak vehicle travel and/or other adjustments to the CTPP's
representation of home-to-work travel? I am aware of one test that notes the
"lumpiness" of working directly with the TAZ-to-TAZ level CTPP data (with the
end result being the %RMSE statistics do not look stellar), but am also aware of many
forecasters who manage to squeeze good value out of whatever ground truth-based data is
available. I am reluctant to bring up the "origi!
n-destination matrix estimation" approach that can start with even a seed matrix of
1's in every TAZ to TAZ cell, but would be happy to hear of any CTPP-based efforts
where the study has summarized how the "raw" CTPP trip table matrix compares to
the final adjusted "seems to assign well" matrix.
I am not expecting to see many responses that focus on use of CTPP in this type of
exercise, and suggest that you reply directly to this listerv rather than just to me,
since whatever info you might offer might inspire others to comment. But if there is some
reason why that may be a problem, I am happy to get your comments directly to the email
noted below (and can send to the full listserv without attribution to you).
Thanks in advance,