Intelligent Transportation Systems (ITS) using the Internet of Things technologies have received great attention as they promise to improve transportation safety in smart cities. The number of road accidents has increased significantly, while the number of vehicles continues to grow. The use of sensors on vehicles allows us to detect and manage the current state of the road accident. In this context, an accident detection and reporting system using IoT technologies and a general ontology modeling the accident context are proposed. The solution uses a custom Android application to capture data related to speed, gravitational force, pressure, shock, and location, etc. Afterwards, the collected data are processed to identify traffic events. Furthermore, the system detects the occurrence of accidents in real time and gives the nearest hospital and concerned authorities useful information about the accident, including the driver's condition and the accident's severity. Simulations and a case study with a real accident dataset obtained from the KSA road safety benchmark validate the proposed approach, which yields promising results in terms of accuracy.