Two critical aspects related to microscopic simulation are discussed: a methodology for calibration and validation, and the integration of path dynamics modeling on large networks. These are among the most significant challenges in microscopic simulation for decision support and analysis in advanced traffic management and information systems. For calibration and validation, a distinction is made between conceptual and operational phases; the conceptual phase concerns the basic models such as car following and lane changing, and the operational phase is associated with the context of the study (origin-destination, parameters adjustments with respect to the network under study, etc.). Then a methodology is described that brings to microscopic simulation the type of capabilities for path processing and storage normally found only with macroscopic models, often because the network representation is less detailed for those. This is based on a hybrid simulation approach. An example of integrating the parallel microscopic simulation with the routing and behavior response simulation schemes, as in the dynamic network assignment simulation model for the advanced road telematics macroscopic model, is used to explain a candidate methodology to enhance microscopic models for evaluating information-routing schemes in advanced traffic management and information systems. Relevant problems faced by advanced traffic management and information systems modelers are raised that are worth further discussion; the intention is not to provide extensive results or even to answer all of the questions raised.