Vehicles’ speed is one of the most significant factors affecting the probability of traffic accidents and the severity of their consequences. The correlation between the number of severe traffic accidents and the operating speed of the traffic flow is particularly pronounced in urban areas. One of the main groups of measures aimed at increasing traffic safety includes the application of various methods and equipment for traffic calming. In recent years, the accelerated development of ITS systems and modern systems based on the application of artificial intelligence can effectively influence the increase of traffic safety. The subject of this research is to analyze the efficacy of an ITS system for automatic display of vehicle speeds and speed-activated traffic lights control which is already in operation on selected road sections in the Republic of Croatia. With the aim of increasing the quality of the results and a proper understanding of the effectiveness of the ITS system, the research included four different categories of traffic flow management in similar traffic situations as well as the traffic-technical characteristics of the road. The research was conducted in areas of isolated pedestrian crossings where, as a rule, higher speeds are expected. The system proved to be effective since it significantly affects the calming of the speed of the traffic flow throughout the day. The 85th percentile speed analysis showed that at locations with implemented ITS traffic calming system, the 85th percentile speeds are, in average, about 17–22% lower compared to other researched different pedestrian crossing type locations. Also, the research shows that the presented solution contributes to the harmonization of traffic flow, which, therefore, has a positive impact on traffic safety.