Analysing car users’ driving behaviour: safety domains for different types of roads

The objective of this paper is to investigate about the driving style in different types of roads, with the final aim to establish some domains of road safety based on speeds and accelerations. We identify a tool that can provide an objective indicator of driving behaviour, represented by the percentage of points outside the domain: the more the percentage of points outside the domain is, the more the driving risk is. The proposed work is supported by an experimental survey consisting in the monitoring of real paths ran by drivers. For each path, the instantaneous speed and acceleration along the pattern were registered by means of GPS-enabled smartphones. Three different roads placed in the South of Italy were analysed, and specifically, a minor rural arterial road, a principal rural arterial road, and a freeway. The registered parameters were used for defining a safety domain which establishes if the driver had a safe behaviour or an unsafe one. The proposed methodology starts from the dynamic equilibrium of the vehicle, and arrives to establish a curve expressing the relationship between the speed and the acceleration vectors, which represent the domain within which the driver behaviour can be considered as safe. Having different formulations concerning the friction factor for the three different kinds of road, we obtained three different curves, or domains. Interesting findings were obtained by comparing the results from the proposed methodology for the different types of roads. As expected, the limits of the domain are quite different among the roads, because each road has its own characteristics.