Analysis of the impact of incoming speeds on roundabout conflicts using microsimulation modelling

Abstract

This study investigated the influence of incoming vehicle speeds on the frequency, typology, and severity of vehicle‑to‑vehicle conflicts at a single‑lane roundabout, employing microsimulation modeling and the Surrogate Safety Assessment Model (SSAM). The roundabout model was held constant in terms of geometric design, and no variations in traffic demand were introduced. Incoming speeds between 30 and 70 km/h, representative of typical operational speeds in urban networks, were systematically evaluated. The findings show that higher incoming speeds increase intersection throughput and enhance operational performance, whereas safety performance remains more favorable at lower speeds. Although no clear functional relationship was observed between incoming speed and the total number of conflicts, a consistent increase in conflict severity metrics (TTC, PET, MaxS) was recorded with rising speeds, indicating elevated interaction risk. These results underscore that the conflict count alone is insufficient for assessing roundabout safety. A comprehensive evaluation requires the integration of multiple complementary indicators that jointly capture both the frequency and severity of surrogate safety events.