RE: travel_data

 Thanks Paul,
I'm also interested to know the name of the travel model you used for
this process, and was wondering if we might be able to adapt this model
for use with the data that we've collected. Is this model used
specifically for travel time data, or does it produce any data that
might be used in other urbansim input tables? If it is specifically for
travel times, what inputs would most likely need to be used, and are
there other models that you use for different purposes?

Cheers,
Adam.

-----Original Message-----
From: Paul Waddell [mailto:pwaddell_at_u.washington.edu]
Sent: Wednesday, 30 May 2007 4:59 PM
To: Adam Rae
Cc: Users_at_urbansim.org
Subject: Re: travel_data

Adam

UrbanSim is generally connected to an existing regional travel model,
from which either composite utilities from the mode choice model (aka
logsums) or more generally, congested travel times by mode for the
home-based-work purpose in the a.m. peak period (or other similar
measures) are extracted for each travel model year. The connections can
be automated - we have done this with emme/2 and transcad most recently,
and previously with TP+ and Minutp. It essentially requires an
interface to be written for whichever travel model you are using, to
summarize UrbanSim output and generate the inputs required for the
travel model; and in the other direction, to extract travel model
outputs and generate the travel_data table -- with whatever travel
measures you want to use. Logsums are by no means required, and we have
found them to be somewhat unstable in practice (though they look good in
theory) - with small changes in the travel model causing large shifts in
the logsum measures and therefore precipitating a recalibration of
UrbanSim.

Paul

Adam Rae wrote:
> I am curious as to what method might be used to obtain the figures
> under the 'logsum' fields in the travel_data table?
> If anyone could inform me about how they generated these figures when
> they were filling in this table it would be greatly appreciated.
> Thanks,
> Adam.
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Received on Wed May 30 2007 - 01:16:05 PDT