Influence of drivers' psychological risk profiles on the effectiveness of traffic calming measures.

Road traffic injuries represent a serious public health problem and are one of leading cause of death, injury and disability around the world. Road accidents are often caused by an accumulation of factors; however, drivers appear to be by far the most decisive one. The driver's behaviour is complex and depends on reflex (or involuntary) and voluntary driving actions. The first class of actions (reflex actions) are typical human reactions that remain inaccessible to awareness and refer to the direct interaction between the road user and the characteristics of the road and its surrounding environment. Conversely, voluntary actions are conscious behaviours adopted on the basis of planned decisions. Both types of driving actions act simultaneously and the interaction between them and their relative effects on road safety are an aspect not yet well examined. The main objective of this study was to provide, by means of a driving simulation experiment, an insight on this interaction by evaluating the influence of some psychological characteristics on the effectiveness of different types of traffic calming measures at pedestrian crossings, designed according to the Human Factors principles. Fifty-eight participants drove a virtual urban route while data on their performance, as they approached five configurations of pedestrian crossings equipped with different physical and perceptual treatments, were collected. The participants were preliminarily characterized by means of two psychological questionnaires, which allowed the identification of three distinct groups of drivers belonging to three risk profiles (careful, worried, and at risk). The three groups of drivers reacted differently to the proposed engineering treatments, confirming the clustering identified by the preliminary analysis. The results showed that the proposed traffic calming measures are effective on all psychological sub-groups of drivers, with different effectiveness. These first results support that, in the considered driving environment (pedestrian crossings), the Human Factors approach, with which traffic calming measures can be arranged, could be effective, even if different psychological sub-groups are differently affected.