The possibility of using some warnings inside modern vehicles should be an aid to the driving activity. However, the information transferred to users is not always received in the expected way due to the variability and complexity of the road environment. This study, therefore, aims to identify a procedure that allows to ascertain whether drivers receive the data in an appropriate way even during particular manoeuvres, such as passing cyclists on a winding road or, on the contrary, if they represent an unnecessary overload. To answer this question, an experimentation in a simulated environment was set up with which the drivers’ visual behaviour was recorded in presence and absence of a driving aid device (On- Board Unit, OBU). The results show that, in some situation, the information provided by the OBU helps to maintain a more virtuous driving behaviour but, in the most complex ones, drivers acquire information from a smaller number of sources, excluding the aid devices present inside the cockpit. This procedure is useful for ADAS designers in order to refine these instruments but also for road managers who can improve safety by inserting appropriate signs or speed limits.