[CTPP] RE: A Question - work flow vs. HBW trip rate

Mon Nov 10 13:37:56 CST 2008

Elaine and Ed,

Thank you very much for your answers. They are very helpful.

One more question on this issue. In Eric's explanation- "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." Does he mean comparing "750 trip" to the "CTPP workers"
?

Thanks a lot!

Binbin

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Today's Topics:

   1. Re: ctpp-news Digest, Vol 57, Issue 1 (Out Of Office Auto
      Message) (John Posey)
   2. RE: A Question - work flow vs. HBW trip rate (Murakami, Elaine)
   3. Re: A Question - work flow vs. HBW trip rate (Ed Christopher)
   4. Quick TAZ Update  (Ed Christopher)
   5. Diana Portillo is out of the office. (Diana Portillo)

----------------------------------------------------------------------

Message: 1
Date: Fri, 07 Nov 2008 12:04:59 -0600
From: "John Posey" <john.posey at ewgateway.org>
Subject: [CTPP] Re: ctpp-news Digest, Vol 57, Issue 1 (Out Of Office
	Auto	Message)
To: <ctpp-news at chrispy.net>
Message-ID: <s9142ef8.080 at nws-ewg4.ewgateway.org>
Content-Type: text/plain; charset=US-ASCII

I will be out of the office until November 17.  Please contact Hilary
Perkins if you need assistance before then.  

------------------------------

Message: 2
Date: Fri, 7 Nov 2008 11:27:29 -0800
From: "Murakami, Elaine" <Elaine.Murakami at fhwa.dot.gov>
Subject: RE: [CTPP] A Question - work flow vs. HBW trip rate
To: <ctpp-news at chrispy.net>
Message-ID:

<195CBC4D6D4C1547BFCE1198D7D6633977AA51 at fhxwa4.fhwa1.fhwa.dot.gov>
Content-Type: text/plain; charset="us-ascii"

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 at chrispy.net
[mailto:ctpp-news-bounces at chrispy.net] On Behalf Of Binbin Chen
Sent: Thursday, November 06, 2008 2:18 PM
To: ctpp-news at 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

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Message: 3
Date: Fri, 07 Nov 2008 14:17:07 -0600
From: Ed Christopher <edc at berwyned.com>
Subject: Re: [CTPP] A Question - work flow vs. HBW trip rate
To: ctpp-news at chrispy.net, eric pihl <eric.pihl at dot.gov>
Message-ID: <4914A243.1080409 at berwyned.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

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 at 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

------------------------------

Message: 4
Date: Fri, 07 Nov 2008 14:21:35 -0600
From: Ed Christopher <edc at berwyned.com>
Subject: [CTPP] Quick TAZ Update 
To: ctpp-news maillist <ctpp-news at chrispy.net>
Message-ID: <4914A34F.5070008 at berwyned.com>
Content-Type: text/plain; charset=windows-1252; format=flowed

Earlier this week the AASHTO CTPP Oversight Board met and reached an 
agreement on TAZs for ACS.  MPOs and states wishing to create TAZs will 
be able to do so during the summer of 2011.  This is a change from the 
previous schedule (spring of 2009) and now gives everyone more time 
along with the benefit of knowing what the block level 2010 population 
counts will be when making TAZs.  Stay tuned for more details.

In other news from the Census Bureau...
American Community Survey 2005-2007 Data Release - On Dec. 9, the Census
Bureau will release the first set of three-year American Community 
Survey data for all geographies with populations greater than 20,000. 
The release will provide the first look at detailed socioeconomic and 
housing characteristics for geographies between 20,000 and 64,999 since 
Census 2000.  (Data will be embargoed to the media Dec. 4.)

-- 
Ed Christopher
708-283-3534 (V)
708-574-8131 (cell)

FHWA RC-TST-PLN
19900 Governors Dr
Olympia Fields, IL 60461

------------------------------

Message: 5
Date: Fri, 7 Nov 2008 15:31:44 -0800
From: Diana Portillo <diana_portillo at dot.ca.gov>
Subject: [CTPP] Diana Portillo is out of the office.
To: ctpp-news at chrispy.net
Message-ID:

<OF4EB1236F.FDC0B82D-ON882574FA.00813FC9-882574FA.00813FC9 at dot.ca.gov>
Content-Type: text/plain; charset=US-ASCII

I will be out of the office starting  11/07/2008 and will not return
until
11/13/2008.

------------------------------

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