Because vessel traffic in ports and waterways is growing quickly, much attention has been given to maritime traffic safety and port capacity. Many simulation models have been used for predicting traffic safety and port capacity in ports and waterways. However, maritime traffic models have considered only a few aspects; the influence on safety of human behavior and external factors has not been included. An analysis based on data from an automatic identification system was performed under various external conditions in an investigation of vessel behavior and external influencing factors. The study area included a junction and a slight bend with high maritime traffic density within the port of Rotterdam, Netherlands. Vessels were classified according to type and gross tonnage. Equidistant cross sections approximately perpendicular to the navigation direction were used for investigation of vessel behavior, including speed, course, and path for each vessel category. The influence of external factors (wind and visibility) on vessel behavior was identified through a comparison with the behavior of unhindered vessels. In the analysis, specific thresholds were set for selecting external conditions and eliminating the influence of encounters. The analysis of unhindered vessels for each vessel category provided insight into vessel behavior. The results revealed that wind had an influence on vessel speed and that visibility affected vessel speed, course, and path. Analysis results can be used as input for the development of a new maritime traffic model, as well as for its verification and validation.