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SIMULATING ROUNDABOUTS WITH VISSIM

The purpose of this paper is to inform traffic engineers about the power and flexibility that VISSIM offers in analyzing roundabouts. Typically, traffic engineers use "static" analysis software (such as aaSIDRA) to analyze the expected traffic operations at roundabouts. There are certain projects, however, where traffic simulation should be considered to assess the traffic operations of roundabout alternatives. The "static" software packages can only analyze individual intersections as independent entities and thus ignore the system impacts of roundabouts. Traffic simulation is increasingly being used to assess traffic operations along many different types of roadway networks. From highways to arterial streets, traffic simulation enables the engineer as well as the public to visualize traffic operations. Roundabouts, however, have unique operational characteristics that some existing simulation packages do not currently model very well. VISSIM has considerable flexibility and can simulate many of these characteristics. HDR Engineering, Inc., recently used VISSIM to analyze traffic operations for two very different roundabout projects. The first project included the analysis of six proposed two-lane roundabouts along Missouri Avenue in St. Robert, Missouri, while the other project included the analysis of a proposed "dumbbell" arrangement along Missouri Route 367 just outside the City of St. Louis, Missouri. VISSIM was used on both projects due to its excellent graphical capabilities and its ability to model roundabouts through user-defined parameters. The following VISSIM features and their importance in effectively simulating roundabouts are covered in this paper: link and connectors, routing decisions, reduced speed zones, and priority rules.