The Municipality of Rome plans to introduce a taxi-bus system as a night service. A micro-simulation model was developed to estimate the needed information. Two major topics regarding this model are presented. First, the iteration process for input parameters is described. The number of potential customers is determined by means of an external modal split model. Two input parameters (frequency of trips and travel times) for the external model are estimated by the micro-simulation model. An iteration process was used. The second topic is the integration of an optimization model into the micro-simulation model. Both simulation and optimization components were implemented in the simulation system SLX