Traffic quality and safety on road transport systems depend on the numbers of users on the system and the nature and quantity of perturbations present. Such perturbations (Russo and Viteea, 1996) must be classified in order to define analytical methods and tools which may be associated to each kind of perrturbation (Fig. 1). As regards the cause of the perturbation, this may be either endogenous or exogenous to the traffic flow. There are endogenous causes when several vehicles use a road section at the same time and are interdependent. Exogenous causes depend on factor external to the flow. They may be due to problems tied to the specific geometry of the links or the topological network configuration. They happen in relation to various causes (accidents, demonstrations, etc.) or to normative conditions established by the system manager, such as total or partial, closure, of certain areas of the network due to problems of system management (the exceeding of permitted congestion limits, ordinary or extraordinary maintenance works, etc.).
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