Safety valuation methods at urban atypical intersections. Analysis of infrastructural scenarios

The definition of decision support tools for identifying ex ante evaluation issues for road safety measures is a new challenge for policymakers and designers managing road networks with the intention of improving traffic safety for roads of their competence. This is consistent with explicit strategies on sustainability in the transport sector established at European level, considering road safety as an essential prerequisite to warrant a sustainable mobility. Based on these considerations, the need for evaluation instruments of safety conditions both for existing infrastructural schemes and for new road installations is recently arisen so that the identification of risks involved in a particular road infrastructure is easier, as well as the definition of the priorities of intervention by means of technical measures. This is true in particular for road junctions characterized by a configuration not conforming to those ones recognized as safer. On this regard, the results of safety evaluations at roundabouts are not an exhaustive reference for geometric design where organizational schemes for circular intersections are similar to roundabouts but resulting from compromise choices as regards one or more geometric features of the roundabout. For this kind of atypical intersections specific safety problems are found, particularly in urban areas, due to existing constraints of different kind and the great variety of geometric layouts they take on. Moreover, in these cases the possibility of applying the safety methods proposed in the literature regarding traditional roundabouts, as well as the road safety audit procedures, is also compromised. Based on these considerations, in this paper ten case studies of this kind of intersections have been examined in order to verify the effectiveness of the risk analysis proposed by means of an infrastructural scenarios method. From the methodological point of view, the application of the accident delocalization procedure has allowed to highlight in relative terms the riskiness of different infrastructural scenarios arranging the organizational schemes of intersections. Moreover, the proposed method can represent a useful tool for safety diagnostic analysis being able to provide informations for policymakers and designers in order to address the infrastructural scenarios and the road schemes that need to be tested