Safety and Operational Performance of Signalized Roundabouts: A Case Study in Doha

Abstract

Traffic safety is one of the important challenges that urban transportation systems are facing. The common practice of assessing the safety of transportation systems starts with the collection of readily available crash data and crash reports from different resources, processing these collecting data. This approach, however, requires having an operational transportation system and historical crash data that are extended for long periods that can, which are usually years before proper assessment and proposed countermeasures can be implemented. Therefore, a new trend in analyzing and assessing the traffic safety of different transportation systems has been developed and used lately. This trend relies on analyzing traffic conflicts that are generated through traffic simulation environment. Those simulated traffic conflicts are then associated with different traffic safety assessment measures. The simulated traffic conflicts can be obtained by analyzing observed vehicle trajectories, or simulated ones. Surrogate Safety Assessment Model (SSAM) is an analysis tool that processes simulated traffic trajectories. In this paper, the safety and operational performance of a signalized roundabout in the City of Doha ate assessed through the simulation approach and applying the surrogate safety assessment model. The results indicated that the signal timings and phasing schemes are associated with the level of safety at the signalized roundabout by reducing or increasing the potential traffic conflicts. Moreover, it was found that high traffic demand at signalized roundabouts is not necessarily related to the high traffic conflicts or high conflict severity.