Combining speed and acceleration to define car users' safe or unsafe driving behaviour

Among all the available methods in the scientific literature, a way for characterizing driver behaviour is the g-g diagram, that shows the longitudinal and lateral accelerations on the y and x-axes, normalized with respect to gravity, recorded on a vehicle during a real test on the road. However, we retain that also speed has to be considered for characterizing drivers' behaviour, being acceleration and speed strictly interrelated. Starting from the g-g diagram, we propose a methodology which describes the relationship between lateral and longitudinal accelerations and speeds, and represents a tool to classify car drivers' behaviour as safe or unsafe. An app for smartphone allows the geo-referenced kinematic parameters of the vehicle to be detected. The experimental survey supporting the methodology was carried out on a rural two-lane road in Southern Italy.