MTSS -- a marine traffic simulation system and scenario studies for a major hub port. Hub ports need to ensure that their navigational networks can fulfill increased demand in marine traffic. They also need to assess the possible impacts of an accident resulting in partial or complete closure of navigation channels. For lack of adequate analytical tools, modeling and simulation are the only means for such studies. To date, however, no adequate simulation tool exists for modeling and simulating the complex traffic at a large-scale hub port. The challenge is to efficiently model the large number of interacting vessels while accurately reflecting the navigational behaviors of various types of vessels whose movements must comply with prevailing protocols in a location- and situation-aware fashion. We present a systematic approach that enables the construction of a marine traffic simulation system called MTSS. MTSS was calibrated based on detailed analysis of historical records obtained from a major hub port, and it was validated by the domain experts. MTSS was used in a capacity study of marine traffic at a hub port that is unique in the scale and complexity of its waterway networks, the intricacies of its traffic patterns, and the required accuracy of the navigational behaviors of different types of vessels. The usefulness of MTSS is further demonstrated by applying it to assess the impacts of partial closure of a waterway under an emergency scenario. For large-scale hub ports, MTSS now opens up new possibilities of realistic scenario studies and disruption management.