Incorporating Vertical Acceleration for Defining Driving Behaviour

Acceleration of a vehicle is composed of three components: longitudinal, lateral, and vertical acceleration. Longitudinal and lateral accelerations have been frequently considered as components for investigating driving behaviour, with the aim of improving road safety. But in particular situations during the motion of the vehicle, also vertical acceleration is relevant. In this paper, the authors want to demonstrate that vertical acceleration is also a relevant parameter to be considered in terms of road safety. The authors focus on the difference registered by considering only lateral and longitudinal acceleration and by considering also vertical acceleration in the analysis of driving behaviour through real tests on the road. All the parameters were registered through a global positioning system (GPS) device and a tri-axial accelerometer, which allow the geo-referenced kinematic parameters of the vehicle to be detected. For this purpose, over 110 tests covering about 600 kilometers were completed. All the experimental surveys were conducted in a good weather condition, under dry road pavement conditions, on weekdays, during day time and out-of-peak hours, in order to have no influence from the traffic flow. Each path was repeatedly run by the driver in order to collect the instantaneous speed and acceleration along the pattern. During the tests, about 40,000 instantaneous values of vehicle position have been registered. The survey interested a segment of the Italian National road n.107 (S.S. 107), in Southern Italy. The authors found that by considering vertical together with longitudinal and lateral accelerations, a higher number of unsafe driving conditions can be identified. More specifically, the proposed methodology allows 20% extra of dangerous driving conditions to be registered. For this reason, the authors retain that also vertical acceleration should be considered in the definition of the safety domain, because it determines the intensity of the exchange forces between the tires and road pavement, and in some cases, it leads to a loss of friction. Definitively, the authors retain that vertical acceleration is not only useful as indicator of comfort on board, but it has an important role also in terms of road safety.