18-25 Nambisan Feature.indd

INTRODUCTION Traffi c circles have been a part of the U.S. transportation system since the early 1900s. However, traffi c circles faded away from the transportation scenario because of high accident and congestion rates due to the priority given to vehicles entering the intersection. It was not until the adoption of the “modern roundabout” in the United Kingdom during the 1950s that new meaning was given to the circular intersection design. Modern roundabouts refl ect a number of improvements over traffi c circles, such as entering vehicles yielding to circulating traffi c; the addition of a splitter island; and no crosswalks in the circulating path. Since 1990, the United States has witnessed increased use of roundabouts, in part due to their potential advantages over STOP-controlled intersections in terms of safety and capacity. The general thought about roundabouts is that they increase the safety characteristics of an intersection by reducing confl ict points and, overall, lowering the speeds of circulating and through vehicles. The objective of this feature is to present the results of a safety analysis of roundabouts in comparison with conventional STOP-controlled and signalized intersections. These roundabouts and intersections are located in the Las Vegas, NV, USA, metropolitan area. Crash data for a 5-year period are used for the study, and the comparison of intersection controls is done with respect to the time of crash, contributing factors, type of crash and roadway conditions. Some statistical tests also are performed to evaluate the signifi cance of the results.