  Microsimulation based frameworks have become very popular in many research
areas including travel demand modeling where activity-based models have been in
the center of attention for the past decade. Advanced activity-based models
synthesize the entire population of the study region and simulate their
activities in a way that they can keep track of agents resources as well as
their spatial location. However, the models that are built for these frameworks
do not take into account this information mainly because they do not have them
at the modeling stage. This paper tries to describe the importance of this
information by analyzing a travel survey and generate the actual alternatives
that individuals had when making their trips. With a focus on transit, the
study reveals how transit alternatives are limited\unavailable in certain areas
which must be taken in to account in our mode choice models. Some statistics
regarding available alternatives and the constraints people encounter when
making a choice are presented with a comprehensive choice set formation. A mode
choice model is then developed based on this approach to represent the
importance of such information.
