Impact of Geometric Parameters and Operational Speed on Traffic Safety at Roundabouts: A Conflict Analysis Using Microsimulation Models

This study examined the impact of geometric parameters and operational speed on traffic safety at single-lane, medium-sized urban roundabouts, utilising microsimulation models. Using data from nine roundabouts in Rijeka, Croatia, the research explored the relationship between roundabout design, vehicle speed and potential conflicts. Unlike traditional approaches reliant on historical crash data, this study employed a combination of microsimulation and the Surrogate Safety Assessment Model (SSAM) to assess safety impacts even in the absence of comprehensive crash records. Key findings revealed that geometric elements such as entry and exit widths, central island size, and circulatory road width substantially affect vehicle speeds and conflict occurrence. While wider entries and exits reduce conflicts, larger central islands are linked to higher frequencies of rear-end conflicts. The study underscores the importance of tailoring roundabout designs to local traffic conditions to enhance safety by controlling vehicle speeds and reducing conflict points.