2. Travel Demand

Instead of the traditional Origin-Destination matrix definition used in the demand formulation of traffic microscopic simulation models, SimMobility ST uses an activity-based demand formulation. In such approach, the trip-chains are generated by individual daily schedules instead of aggregated traffic specific matrices. Such data can be obtained directly using mobility and goods survey data or using a pre-day simulator, such as the one integrated in the SimMobility Mid-term framework. This framework consists of an activity-based modelling system formulated as interconnected discrete choice models representing choices at distinct dimensions. This Pre-day model development follows the Day Activity Schedule approach, which focuses on decisions related to daily activity and mobility. There are three different hierarchies in the system:

• day pattern level
• tour level
• intermediate stop level

Each level consists of several models. Given the complicated and multidimensional nature of the day activity schedule problem, the curse of dimensionality will occur if every choice dimension is put into one single choice model. Therefore, choice dimensions are isolated, structured, and put into different choice models. The overall system can be viewed as a hierarchical (or nested) series of choice models.