Safety is a prevalent issue in intelligent transport systems (ITS). To ensure such a vital requirement, methodologies must offer support for the careful design and analysis of such systems. Indeed these steps must cope with temporal and spatial constraints associated with mobility rules and parallelism which induce a high complexity. Here we handle the problem of unexpected and uncontrollable vehicles which significantly endanger the traffic. In this context, we propose to apply discrete control theory to a model of automatic motorway in order to synthesize a controller that handles collision avoidance. This approach includes two parts: the design of a formal model and an efficient implementation based on hierarchical decision diagrams.