As part of a study by TMIP, new incremental improvements were made to the Salt Lake City metropolitan area’s trip-based travel model to improve the handling of non-home-based trips. These techniques are designed to be inexpensive enhancements to existing trip-based models that can be implemented quickly in a straightforward manner as part of a model update without requiring the development of a whole new model.

The methods tested in the Salt Lake region are intended to address fundamental problems with the accuracy and response properties of non-home-based trips in trip-based models. These problems can be understood in a variety of ways, but ultimately are related to the inconsistency of the four-step model with tours and the fundamental fact that in order to properly represent non-home-based trips, two spatial distribution models are required to account for both the trip’s origin and destination (whereas the four-step model architecture produces non-home-based trips from only one trip distribution model). The fundamental approach to addressing these issues in the methods tested is to adopt an alternative trip-based model architecture in which non-home-based distribution is run in series rather than in parallel with home-based distribution models. This relatively simple structural change may significantly improve trip-based models’ ability to represent non-home-based trips and their response to land use changes and transportation infrastructure investments.

This presentation will both illustrate the basic methods and share the results of several different types of sensitivity tests / potential applications such as new land use development, new highway and new transit investments.

While activity-based models offer one existing alternative to trip-based models with improved handling of non-home-based trips, for a variety of reasons from costs to staff skills, many agencies are unable or uninterested in replacing their trip-based models with activity-based models. The methods tested in Salt Lake City may also offer other agencies another option for addressing issues related to non-home-based trips in traditional models.