Roundabout Analysis in VISSIM

The Texas Department of Transportation (TxDOT) and Civil Engineering Consultants (CEC) commissioned a traffic operations and impact analysis for the intersection of US 271 and proposed FM 1000/Tennison Road connection in Mount Pleasant, Texas, approximately 120 miles east of Dallas. The primary objective was to determine the traffic operations benefits of a roundabout in lieu of a signalized intersection. Lockwood, Andrews, & Newnam, Inc. (LAN) developed four alternative intersection layouts and analyzed them using VISSIM traffic simulation software. A key technical issue in this project was developing proper vehicle interaction between the vehicles entering the roundabout and the vehicles inside the roundabout. Analyzing a roundabout requires reasonable vehicle interaction because too aggressive behavior will overstate capacity; too passive behavior will understate roundabout capacity. Software parameters must be fine-tuned to model vehicle interaction. This problem is compounded in the Mount Pleasant effort because the proposed multilane roundabouts have more complex vehicle interactions than a single lane roundabout. VISSIM analysis of the three roundabout alternatives and signalized intersection showed that a signalized intersection will result in lower delays in future years than the roundabout alternatives. The roundabout alternatives impeded the high through movements on US 271, and vehicles on FM 1000/Tennison Road incurred delays waiting for an acceptable gap in traffic. This paper presents the results of this analysis and a detailed explanation of the modeling techniques in VISSIM that allowed a realistic analysis to be performed.