This paper presents the stages in stochastic ship traffic stream model creation, applied to determine the influence of liquefied petroleum gas (LPG) tanker introduction to Police Port on the Świnoujście–Szczecin waterway. The model is based on the Monte Carlo methodology, and is microscopic (which means that each ship’s model is treated as a separate object possessing given attributes). The model is applied here in order to find the influence of ships with dangerous cargo (LPG tankers in the case study) on regular ship traffic, and hence to establish whether special traffic solutions are necessary.