Roundabouts are widely used to reduce the severity of conflicts at intersecting roads. While they tend to provide an acceptable level of traffic operation, their operational benefits are reduced when traffic demands increase. One possible and economic mitigation is to convert the roundabouts into signalized ones to accommodate the demand increase and to further reduce the conflicts. This conversion will allow the roundabouts to perform both functions (safety and operational) within acceptable levels. Accordingly, proper signal timing parameters are often required to achieve the anticipated safety and operational levels. Unlike the operational performance of signalized intersections that can be easily assessed based on field measurements, safety assessment is far more difficult due to the need of historical crash data, which would potentially take years. This study presents the use of traffic simulation to assess the operational performance as well as the safety performance of signalized intersections. At first, a well-calibrated model of a signalized roundabout located in the city of Doha is built in microscopic traffic simulation environment based on field measurements and observations. Secondly, Surrogate Safety Assessment Method (SSAM) is used to analyze the simulated vehicular trajectories to identify the type and severity of conflicts. The results revealed that the implemented signal timing parameters have a significant impact on the safety functionality of the signalized roundabouts.
Operational Performance and Safety Assessment of Signalized Roundabouts