This paper presents a semantic approach for route determination and support for several vehicles sharing the same environment. This approach relies on designing ontologies that use a semantically rich mark-up language (OWL – Ontology Web Language) and the SWRL (Semantic Web Rule Language) rule expression set. A real-time ontology update procedure is also proposed to face unforeseen circumstances. In particular, it has been implemented in a real prototype using an ACO (Ant Colony Optimization) metaheuristic to detect road width variations. Several road crossing configurations have been tested in order to check the performance of the system. The times to calculate the route and resolve priorities at crossings allow the vehicles to navigate in real-time