Infrequent Events in road tunnels (fire, accidents, etc.) lead to high risk situations that can endanger many lives and cause great materials damage. These events are so varied and often unpredictable that it is difficult to make correct decisions due to the lack of initial information and the rapid change in the event progress. The development of a Decision Support System (DSS) in road tunnels will permit a suitable emergency management and it will ensure the minimization of personal damages in these kind of events. The system will be formed by three fundamental elements: the Infrequent Events Model. The Evacuation Model has been developed based on the Black-Box Model, Boolean algebra and Probability Theory defining the inputs, the outputs and the main parameters. The mathematical equations which relate inputs, outputs and main parameters have been obtained. The development of the computational model and the auxiliary programs has permitted to verify and validate the model.