In the simulator the route choice model and the route switching model can be used either individually or jointly. The route choice model requires no explicit storage of vehicle paths, thus allows the simulator to be used effectively with minimal memory requirements for large networks. The route switching model is designed to support the simulation of ITS applications with ATIS elements. Since a path table is pre-specified in this approach, calculation of time-dependent shortest paths can be avoided. The route switching model requires enumeration of all usable paths. To define the paths considered as choice alternatives by the users, two approaches may be followed [Cascetta et al.(1996)]:
The ``exhaustive'' approach can generate unrealistic routes and is computationally expensive, especially for large networks. In the ``selective'' approach this drawback can be avoided if the conditions and rules for selecting path subsets are well defined.
More sophisticated models that incorporate other considerations in making route choice decisions can also be used [Cascetta et al.(1992), Cascetta et al.(1996)]. The modular design of the simulator allows for easy substitution of the default models.