This paper presents a traffic monitoring system implemented through Wireless Sensor Network (WSN) technology within SAFESPOT Project funded by the European Community. The aim of this project is to provide a flexible, robust, low-cost and low-maintenance wireless solution for obtaining traffic-related data that can be used for automatically generating safety warnings at black spots along the road network. The WSN consists of one Gateway Node (GN) and n Sensor Nodes (SNs) deployed along the roadside according to an approximately linear topology. Each SN is able to monitor a section of road, collecting parameters such as vehicle count, speed and direction. Data from the SNs is collected by the GN and delivered to a Road Side Unit (RSU) responsible for fusing it with traffic-related data generated by alternative sources. The system has been tested and performance evaluated under a number of real use-case scenarios.