Operational and safety effects of two-lane roads alignment

It is well known that traffic safety is one of the main objective in road design and management. Further, it is widely recognised the importance of operating speeds for design consistency and in order to establish a comprehensive safety strategy for rural roads. Operating speeds depend on geometric features such as lanes and shoulders width, radius of curve (or curvature change rate), longitudinal grade and transverse slope. Although several models are available in literature for the prediction of operating speeds, they are usually road-specific and transportability is an unsolved issue. As a consequence, when the performance level of a two-lane rural road in a given context has to be assessed, researchers and practitioners need to treat the problem of operating speed dependence on section alignment by using proper methodologies and models. In the light of the above-mentioned facts the objectives and the scopes of the paper were the analysis and modelling of the operational and safety performance of a two-lane rural road by means of the comparative study of operating speeds and road alignment. The model was applied to several case-histories, related to typical Italian rural roads. Alignment and actual speeds were analysed and monitored and the entire road was discretized into single stretches. Experiments proved that the formalized model for predicting operating speeds can be useful in analysing, predicting and assessing the safety performance of a rural road, even if some issues still call for further research. Future research will aim to gain a better understanding of the effect of some of the remaining boundary conditions on the relationship operating speeds vs. road alignment.