[CTPP] RE: No Car but Drives to Work Alone

Wed Mar 3 10:39:57 CST 2010

Cliff,

The spreadsheet attachment of your work did not come through so I cannot see what exactly you did to extract the drive alone mode from ACS. In ACS 2009 questions 31 relates to mode. Question 32 relates to number of people in the car, truck, or van. Even though instructions say Q32 should be answered if the respondent picked "car, truck, or van" in Q31, it is not that hard to make a mistake in Q32 answer. The layout of the form also separates these questions in different columns. My point is that the answer to Q32 may not be related to trips asked in Q31. I don't think they could have asked Q32 any better but when you mix trips of the LAST WEEK together, I don't think you will get better answers than what we see now.

To test if the disconnection happened between Q32 and 31, I suggest breaking your query into two sections. First, extract how many workers from 0-car households answered "Car, truck, or van" to Q31 (mode of travel). Second, extract drive alone mode from the pool you selected in the first query. Comparison of these answers may shed some light.

The first part of query can be compared with other travel surveys. I don't have a recent HH survey handy but our transit onboard surveys (Dallas-Fort Worth area) show that about 8% of people from 0-car HHs use some sort of drive access to transit. These can be, of course, shared rides, kiss and rides, borrowed car, and leased car. This will give you some point of comparison.

Apologies for the long email but data issues are generally detail and require explanation.

Arash

Arash Mirzaei, P.E. 
Transportation System Modeling Manager 
North Central Texas Council of Governments (NCTCOG) 
Tel: (817) 695-9261 
Fax: (817) 640-3028 
Email: amirzaei at nctcog.org 

-----Original Message-----
From: ctpp-news-bounces at chrispy.net [mailto:ctpp-news-bounces at chrispy.net] On Behalf Of Cook, Cliff
Sent: Wednesday, March 03, 2010 8:37 AM
To: ctpp-news at chrispy.net
Cc: Shulman, Adam
Subject: [CTPP] No Car but Drives to Work Alone

Thanks to all who responded.  I've summarized, paraphrased and quoted below possible reasons below and added a few comments as appropriate:

1.      Other modes such as bicycling, motorcycles and motor scooters. (I think these are covered by the data in 20068 ACS table B08141 so they are not likely the source of the problem.)

2.      Leased, not owned, autos treated not counted as vehicles "kept for use by members of this household" (This would be a misinterpretation of the ACS question but stranger things have happened.  Other types of respondent errors could be in play here as well.)

3.      Problem with data imputed by the Census Bureau for non-responders.

4.      Using a company car on loan, a zip car a neighbors car, a parent's car or another car sharing service. (ZipCar is popular in Cambridge but I doubt that would cover too many people.  Company cars might explain some but again seems an unlikely explanation for almost 700 commutes out of 48,600. Garaging a car not registered in Cambridge is difficult as we require a resident permit for on street parking and off street parking spaces are few and expensive. Over 60% of the housing stock is rentals, often with no dedicated parking space included in the rent.)

5.      Non-standard work week such as travel to a conference.  (This might be a not insignificant source.  I've always been surprised by the number of local residents who JTW data shows as "commuting to work" in California.)

6.      Based on the 2009 NHTS, the ACS result seems reasonable. In the 2009 NHTS (weighted results), 12% of persons in zero-vehicle households who travelled to work "last week", did so in a vehicle with one person in it.  This works out to be 500k people out of 4,260k.

7.      This phenomenon shows up in NHTS as well and appears to be a very real result of the fact that some share of folks used borrowed cars for travel.  It may be a young adult who doesn't own a car but has one available from dad, folks renting, folks borrowing etc. In consumer expenditure surveys non-car owning households also have non trival auto related expenses for  travel.  It is not uncommon for non-car households to travel more PMT in SOV than on transit.  In consumer expenditure surveys non-car owning households also have non trival auto related expenses for  travel.

Thanks to all for your help!

Cliff Cook
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Original post:

I'm hoping someone can help me address this question from a colleague.  He put together a table from the 2006-2008 ACS showing mode of journey to work by vehicles owned and came up with surprisingly large numbers who do not won a car yet drive alone to work. No doubt, there are a few people who fit this category but my guess is that this largely is the result of either people misunderstanding the question or some sort of coding problem. Here is an excerpt from his email ( the Cambridge here is Cambridge, Massachusetts):

I'm looking at ACS data and specifically at cities and percent workers have no car available.  From that I'm then looking to see how those workers get to work.

The attached worksheet shows my work.  What is strange is that it shows for Cambridge that 6.6% of people without a car available drove alone to work.  The percent is similar to Boston. And NYC has 3.4% of workers with No vehicles available driving alone to work.

So, the question is, how can someone without a vehicle drive to work alone?  Do you have any ideas on this?  It could be someone doesn't own a vehicle, but drives a friend's car to work. Or has no car of their own, but uses a company car to get to work.  But seems like a high number for this.

Can anyone shed any light on this?
-----------------------------------------------------------------------------
Clifford Cook
 Planning Information Manager
  Cambridge Community Development Dept.
   344 Broadway
    Cambridge, MA. 02139
     617/349-4656  FAX 617/349-4669  TTY 617/349-4621
      email => ccook at cambridgema.gov
       web site => <http://www.cambridgema.gov/~CDD/>

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