Entry-Lane Capacity Analysis of Roundabouts in Texas Using VISSIM, SIDRA, and the Highway Capacity Manual

Road safety and traffic congestion are two of the critical issues facing the transportation profession today. As a means to promote safety and efficiency at United States intersections modern roundabouts are becoming more and more common. Over the last ten years, roundabouts implementation methodologies have been developed using data collected at U.S. roundabouts. These methodologies were first published in 2007 as National Cooperative Highway Report 572: Roundabouts in the United States and also in 2010 by the Federal Highway Administration in its second edition of the national roundabout guidelines. This work attempts to enhance aspects of these guidelines related to roundabout operations by exploring the effects of exiting flow, origin-destination patterns, and mean speed on roundabout entry-lane capacity. A methodology for calibration and validation of VISSIM is developed. Capacity results from VISSIM are compared to the Highway Capacity Manual entry-lane capacity curve and results from SIDRA to see how well they predict capacity.