Modern Roundabouts and Traffic Crash Experience in the United States

Roundabouts have become very popular in Australia and many countries in Europe during the past few decades. In the U.S.A., however, roundabouts are just beginning to become an alternative treatment for roadway intersections. In the 1930’s and 1940’s traffic circles were popular in the U.S.A. but many have been converted to traditional control since the 1950’s and 1960’s. Modern roundabouts are different from traditional traffic circles, in that approaching traffic yields right of way to circulating traffic. In this study, an effort was made to collect traffic and traffic crash data for existing roundabouts in the U.S.A., and perform a statistical analysis to determine the effectiveness of roundabouts as a treatment for intersecting roadways. General information regarding thirteen roundabouts located in Maryland, Florida, Nevada and California was collected and is included for the readers use. In addition, six retro-fitted 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%. 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 frequency and mean of accidents at 95% and 99% confidence levels, respectively, between pre-roundabout and post-roundabout periods. This study’s 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 American roundabouts should be conducted in the future when more data is available.