Combining speed and acceleration to define car users’ safe or unsafe driving behavior

Speed and acceleration describe the motion of a vehicle. Therefore, these parameters arefundamental to define the behaviour of a driver. To this aim, it is useful to analyse instantaneousand geo-referenced kinematic parameters of the vehicle recorded by real tests onthe road.Among all the available methods in the scientific literature, a way for characterizing driverbehaviour is the g–g diagram, that shows the longitudinal and lateral accelerations onthe y and x-axes, normalized with respect to gravity, recorded on a vehicle during a realtest on the road. However, we retain that also speed has to be considered for characterizingdrivers’ behaviour, being acceleration and speed strictly interrelated. Starting from the g–gdiagram, we propose a methodology which describes the relationship between lateral andlongitudinal accelerations and speeds, and represents a tool to classify car drivers’ behaviouras safe or unsafe. An app for smartphone allows the geo-referenced kinematic parametersof the vehicle to be detected. The experimental survey supporting the methodologywas carried out on a rural two-lane road in Southern Italy.