6 Nov
2008
6 Nov
'08
4:17 p.m.
Hi,
I'm new in using CTPP data, and am a little confused about the work flow
CTPP provided and work trip.
Basically, CTPP counts workers, not trip. Then can it be used to compute
HBW trip per household? For example, assume 1.5 trips/worker
(NCHRP#365), HBW trip/HH = 1.5*workers/household numbers ?
And How can CTPP work flow compare to NHTS HBW trip rate?
I highly appreciate your help!
Best,
Binbin
7 Nov
7 Nov
5:28 a.m.
Ed: sounds like listing the census questions would help .
Alan E. Pisarski
6501 Waterway Drive
Falls Church Va. 22044
703 941-4257
alanpisarski(a)alanpisarski.com
_____
From: ctpp-news-bounces(a)chrispy.net [mailto:ctpp-news-bounces@chrispy.net]
On Behalf Of Binbin Chen
Sent: Thursday, November 06, 2008 5:18 PM
To: ctpp-news(a)chrispy.net
Subject: [CTPP] A Question - work flow vs. HBW trip rate
Hi,
I'm new in using CTPP data, and am a little confused about the work flow
CTPP provided and work trip.
Basically, CTPP counts workers, not trip. Then can it be used to compute HBW
trip per household? For example, assume 1.5 trips/worker (NCHRP#365), HBW
trip/HH = 1.5*workers/household numbers ?
And How can CTPP work flow compare to NHTS HBW trip rate?
I highly appreciate your help!
Best,
Binbin
1:27 p.m.
Yes, the CTPP 2000 uses the Census 2000 and provides a count of WORKERS
AT WORK. Workers at work is generally at least 10 percent lower than
employment or jobs. Also, the Census 2000 allows a response for only 1
job per worker. http://www.fhwa.dot.gov/ctpp/ctppatwork.htm
NCHRP 365 used results from regional household travel surveys AND the
1990 NPTS. (Page 23)
You might want to take a look at the NHTS transferability project that
FHWA completed a few years ago.
http://nhts.ornl.gov/tools.shtml
The work was done by Oak Ridge National Labs and uses the 2001 NHTS
data, and estimates total person trips, total vehicle trips, and trips
by purpose at the tract level. You need to understand how trip
purpose is coded. I glanced at results for census tracts in one county
in Washington State and HBW were about 12% of total trips. Let's say
that the overall average number of household trips is 9 or 10, then 12%
would be 1.1 to 1.2. The transferability project provides trips rates
by household size and vehicle availability.
However, it is very important to understand that a trip from WORK to
SHOP, and then SHOP to HOME, would not be included as a WORK to HOME
(with 1 stop) in the count of HBW trips.
This is why, using the concept of TOURS and TRIP CHAINING has become
increasingly used in travel demand models. The links below are to Nancy
McGuckin's papers (2001 NHTS and 1995 NPTS) on trip chaining:
http://www.travelbehavior.us/projects_files/Trip%20Chaining%20Trends%20i
n%20the%20US%20TRB%20paper%2005-1716%20(2).pdf
http://nhts.ornl.gov/1995/Doc/Chain2.pdf
Hope this helps.
Elaine Murakami
FHWA Office of Planning
_____
From: ctpp-news-bounces(a)chrispy.net
[mailto:ctpp-news-bounces@chrispy.net] On Behalf Of Binbin Chen
Sent: Thursday, November 06, 2008 2:18 PM
To: ctpp-news(a)chrispy.net
Subject: [CTPP] A Question - work flow vs. HBW trip rate
Hi,
I'm new in using CTPP data, and am a little confused about the work flow
CTPP provided and work trip.
Basically, CTPP counts workers, not trip. Then can it be used to compute
HBW trip per household? For example, assume 1.5 trips/worker
(NCHRP#365), HBW trip/HH = 1.5*workers/household numbers ?
And How can CTPP work flow compare to NHTS HBW trip rate?
I highly appreciate your help!
Best,
Binbin
2:17 p.m.
Binbin--Elaine's response is certainly dead on but your question
prompted a broader discussion that I was having with one of my
colleagues. Here what he had to say. Suffice it to say your local
model and more importantly your local conditions will play prominently.
Ed --
A Work to Home trip would actually be counted as two separate trips --
two HBW productions and two HBW attractions. Using a factor of 1.5,
1,000 employees would generate 1,500 HBW trips; then you'd need to
divide by two to approximate a CTPP-derived home-to-work trip, giving
you 750 trips. This, of course, presumes that travelers will be making
round-trips, when we know that many make stops on the way home from
work. Often rules are applied that reallocate a HBW work trip as two
distinct NHB trips (e.g. with a stop of more than 30 minutes); some
models get around this by specifying trips as a 'journey-to-work', which
can include longer duration stops. The use of the 1.5 scaling factor is
intended to capture chaining, absenteeism, and should be understood to
be a rough approximation that may not accurately reflect local
conditions or the labor market.
In terms of comparing with the NHTS trip rates, the analyst could impose
their own rules in terms of how a HBW trip is defined -- and depending
on NHTS sample size for the area considered, a comparison between the
two may be meaningful and shed light on adjustments to the factor used
to convert flows to trips, thereby producing a more reliable CTPP
derived trip-table.
Eric
eric.pihl(a)dot.gov
Binbin Chen wrote:
Hi,
I'm new in using CTPP data, and am a little confused about the work flow
CTPP provided and work trip.
Basically, CTPP counts workers, not trip. Then can it be used to compute
HBW trip per household? For example, assume 1.5 trips/worker
(NCHRP#365), HBW trip/HH = 1.5*workers/household numbers ?
And How can CTPP work flow compare to NHTS HBW trip rate?
I highly appreciate your help!
Best,
Binbin
> ------------------------------------------------------------------------
--
Ed Christopher
708-283-3534 (V)
708-574-8131 (cell)
FHWA RC-TST-PLN
19900 Governors Dr
Olympia Fields, IL 60461
6367
days inactive
6368
days old
3 comments
4 participants
participants (4)
-
Alan Pisarski -
Binbin Chen -
Ed Christopher -
Murakami, Elaine