[UrbanSim-Users] Accessibility model

From: Mark Kryvobokov <k_mark_at_ukr.net>
Date: Thu, 16 Aug 2007 16:07:24 +0300

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          Hello!
  
We have a question concerning the accessibility model. In Eugene package, the table travel_data contains am_single_vehicle_to_work_travel_time and four logsums. We see from the userlist that logsums were found to be unstable. Is it the reason why we don't see any application of logsums in Eugene models? We don't see also the application of am_single_vehicle_to_work_travel_time. Is it applied somewhere? Is the accessibility model described on p. 18-19 of the Reference Manual and Users Guide used at all in Eugene?
  
Thank you in advance,
Mark
  
Paul Waddell wrote:
> 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.
>
Received on Thu Aug 16 2007 - 06:07:27 PDT