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 Tue May 29 2007 - 23:59:04 PDT