Driver’s perceived discomfort and road safety

Road geometry and traffic conditions influence strongly drivers behaviour. The authors propose a model for the evaluation of driver’s level of discomfort LD locally induced by different road environments and traffic flow conditions. The main theoretical hypothesis behind the model is that a significant indicator of the level of discomfort is computed as proportional to the difference between driver’s desired speed Sd and the operating speed So imposed by local traffic density. To evaluate the level of discomfort for an homogeneous road segment, the variation of road characteristics and traffic conditions in terms of flow and composition must be taken into account. Moreover driver’s desired speed depends on the individual reason of the travel. Therefore, considering a traffic condition, the level of discomfort at a specific road location will assume different value for each flow typology. The greater the difference between driver’s desired speed and flow speed, the higher the level of discomfort. Twenty-five Italian rural two way-two lane road segments have been analysed. Field surveys were needed for data collection. The discrepancies between drivers expectations and operating conditions have been analysed. These data have been correlated with road dependent collisions of each road segment. This paper shows the results and points out the validity and applicability of the model to actual case studies for the evaluation of the expected accident occurrence as a function of the level of discomfort suffered by road users.