The OD flows specified in a scenario are translated into individual vehicles wishing to enter the network at a specific time. Behavioral parameters (e.g. desired speed, impatience in following a slower vehicle, critical gaps in changing lanes, compliance rates to traffic signals and signs, etc.), information accessibility, and vehicle characteristic parameters are randomly assigned to each vehicle/driver combination. MITSIM moves vehicles according to car-following and lane-changing models. The lane changing model distinguishes between mandatory and discretionary lane changing. Once a decision to change lanes is made, a probabilistic gap acceptance model is used to determine whether the desired change can be executed. MITSIM also represents drivers' responses to traffic signals, speed limits, incidents, and delays at toll booths. Merging and turning movements at intersections are also modeled.
Each vehicle in MITSIM has its own destination and a path leading to that destination. Vehicles are moved at a fixed step size along their paths in accordance with various constraints. The information provided by the route guidance system affects drivers' pre-trip and en-route route choice decisions through probabilistic route choice models. These models calculate the probabilities of choosing alternative routes at each intersection (or decision point) as a function of the perceived or provided information.