Modern Roundabouts and Traffic Crash Experience in United States

Abstract

Roundabouts have become popular in Australia and many countries in Europe during the past few decades. In the United States of America, however, roundabouts are just beginning to be recognized as an alternative treatment for roadway intersections. An effort was made to collect traffic and traffic crash data for existing roundabouts in the United States and to perform a statistical analysis to determine the effectiveness of roundabouts as a treatment for intersecting roadways. General information about thirteen roundabouts located in Maryland, Florida, Nevada, and California was collected and is included for readers’ use. In addition, six retrofitted roundabout sites with accident data ranging from 1 to 3 years before and after were analyzed. In all but one case, the reduction in accidents for roundabout sites was in the range of 60 to 70 percent. A chi-squared test and a normal approximation test were performed using the accident data from these six roundabout sites. Both of these tests indicated a significant difference in the reduction of frequency and mean of accidents at 95 and 99 percent confidence levels, respectively, between pre-roundabout and post-roundabout periods. Results, though limited, are encouraging and in line with findings of past European and Australian studies involving roundabouts. Additional studies on the safety performance of U.S. roundabouts should be conducted in the future when more data are available to reinforce these findings.