Road design and human factor interaction: a new evaluation method.

The human factor is the most important element in studying road safety: in fact, the mechanisms involved in perception and in recognition and the decisional processes of the road user directly condition the degree of risks of accidents. The natural unpredictable component of human beings make any inquiry into the behaviour of users difficult to study: clearly, the psychology and the reactions of the driver with a specific road scenario are hard to quantify; however, it is necessary to know them in order to design a road environment which is consistent with what the drivers perceive, with their capacities and their actions. These are the reasons which inspired various studies aimed at identifying the expressive parameters of the behaviour of drivers. The level of risk perceived when driving along certain road stretches is certainly one of the most valid and flexible ones. The average risk trend perceived by the user in a road stretch is certainly an indicator of the homogeneity of the stretch itself, and directly affects the behaviour of the drivers when driving along it. These are the foundations for a method used to analyse the behaviour of the road user; it calls for drawing up a questionnaire-interview, where a representative sample of the population of road users expresses a subjective opinion about the risk level perceived in certain situations and road scenarios, specifying the value on a scale of points. This procedure has made it possible to gather a large amount of numerical data and this data has been submitted to an in-depth statistical analysis which has provided interesting conclusions about psychology and behaviour on the one hand, while on the other hand it has also made it possible to establish a direct relationship - by applying suitable regression models - between the geometrical and environmental features of the road. The latter is an extremely important result, since it represents a first approach to road design which takes into direct account the expectations of the users who are expected to drive along the road. For the covering abstract see ITRD E135448.