Analysis of a Road/Tramway Intersection by the ORIS Tool

Intelligent Transportation Systems for urban mobility aim at the grand objective of reducing environmental impact and minimize urban congestion, also integrating different mobility modes and solutions. However, the different transportation modalities may end in a conflict due to physical constraints concerned with the urban structure itself: an example is the case of intersection between a public road and a tramway right-of-way, where traffic lights priority given to trams may trigger road congestion, while an intense car traffic can impact on trams’ performance. These situations can be anticipated and avoided by accurately modeling and analyzing the possible congestion events. Typically, modeling tools provide simulation facilities, by which various scenarios can be played to understand the response of the intersection to different traffic loads. While supporting early verification of design choices, simulation encounters difficulties in the evaluation of rare events. Only modeling techniques and tools that support the analysis of the complete space of possible scenarios are able to find out such rare events. In this work, we present an analytical approach to model and evaluate a critical intersection for the Florence tramway, where frequent traffic blocks used to happen. Specifically, we exploit the ORIS tool to evaluate the probability of a traffic block, leveraging regenerative transient analysis based on the method of stochastic state classes to analyze a model of the intersection specified through Stochastic Time Petri Nets (STPNs). The reported experience shows that the frequency of tram rides impacts on the road congestion, and hence compensating measures (such as sychronizing the passage of trams in opposite directions on the road crossing) should be considered.