On your question #1: One thing to keep in mind relates to the fact that a
"HBW trip" for modeling purposes represents a trip end, e.g., a Home to Work
trip and a Work to Home trip would actually be counted as two separate
trips, i.e., HBW productions and two HBW attractions.
So, using your NCHRP example, 1,000 employees would generate 1,500 HBW
trips--but only half of these (750) would be comparable to a CTPP-derived
home-to-work trip.
In terms of why travel survey data never supports 2.0 HBW trips per
employee: It is partly because of absenteeism on an "average" weekday,
partly because some jobs are simply not five-day-a-week jobs, and partly
because some (or even many) people don't actually go straight from home to
work (or from work to home) on their surveyed day (e.g., they engage in some
trip chaining, which turns some Home-to-Work trips into HNW and NHB trips,
and turns some Work-to-Home trips into NHB and HNW trips).
Hope this helps!
sincerely,
Ken Cervenka
NCTCOG
-----Original Message-----
From: ctpp-news-bounces(a)chrispy.net
[mailto:ctpp-news-bounces@chrispy.net]On Behalf Of Jiji Kottommannil
Sent: Monday, August 16, 2004 12:09 PM
To: ctpp-news(a)chrispy.net
Subject: [CTPP] CTPP Part 3
Hi All,
I am a new user of the CTPP data and am in the process of comparing CTPP
part 3 tract-tract worker flow data to the Home-Based Work trip table
from the travel demand model I am currently working on. I came across a
few questions/issues for which I would welcome your
thoughts/experiences:
1) Do the CTPP part 3 flows account for all the home-based work trips? I
noticed that the commonly accepted home-based work attraction rate is
about 1.5 trips per total employment (NCHRP 365) and this creates more
HBW trips than there are in the CTPP part 3. Let me know if I there is
something wrong in my interpretation of the data.
2) How much success have the MPO's had in calibrating their trip
distribution models based on CTPP Part 3? What level of accuracy is
typically desired?
Thanks!
Jiji
Jiji V. Kottommannil
Transportation Modeling Specialist,E.I.T.
Crawford Bunte Brammeier
Phone: 314-878-6644, Ext. 38
Fax: 314-878-5876
_______________________________________________
ctpp-news mailing list
ctpp-news(a)chrispy.net
http://www.chrispy.net/mailman/listinfo/ctpp-news
Hi All,
I am a new user of the CTPP data and am in the process of comparing CTPP
part 3 tract-tract worker flow data to the Home-Based Work trip table
from the travel demand model I am currently working on. I came across a
few questions/issues for which I would welcome your
thoughts/experiences:
1) Do the CTPP part 3 flows account for all the home-based work trips? I
noticed that the commonly accepted home-based work attraction rate is
about 1.5 trips per total employment (NCHRP 365) and this creates more
HBW trips than there are in the CTPP part 3. Let me know if I there is
something wrong in my interpretation of the data.
2) How much success have the MPO's had in calibrating their trip
distribution models based on CTPP Part 3? What level of accuracy is
typically desired?
Thanks!
Jiji
Jiji V. Kottommannil
Transportation Modeling Specialist,E.I.T.
Crawford Bunte Brammeier
Phone: 314-878-6644, Ext. 38
Fax: 314-878-5876
All,
The CTPP Part 2 final version ASCII files have been released through the BTS Tanstats website. To download these files, please go to: http://www.transtats.bts.gov.
The CTPP 2000 Part 2 - AT PLACE OF WORK tables are organized into two distinct groups: Characteristics of All Workers and Characteristics of Workers in Households. Data documentation and SAS programs are provided in the zipped folder for each state.
Pheny Z. Smith, Ph. D.
Statistician
Office of Advance Studies
Bureau of Transportation Statistics
The note below is from Joe Salvo, who is a very active member of the Census Bureau State Data Center (SDC) network, but not a CTPP listserv member:
We have taken a close look at the counts of total workers from the 1990
and 2000 CTPP Part 2 at the Census Tract level. There seems to be an
unusual amount of volatility, with double-digit percent increases and
declines. (And, it is not a function of small bases, as many of the
tracts showing large increases/declines have several thousand workers.)
We have mapped the changes and, with the exception of two or three
areas, these "ups and downs" seem almost randomly distributed.
Has anyone else compared 1990 and 2000 CTPP data for small areas?
Joe Salvo
NYC Department of City Planning
jsalvo(a)planning.nyc.gov
