Abstract

Because of its historically good performance in many European countries, roundabout has been promoted in the United States since 1990’s. Generally roundabout provides an opportunity to improve traffic flow efficiency and reduce traffic conflicts when designed and located appropriately. Louisiana currently has 25 roundabouts in operation and more than couple of hundreds of roundabouts in design and planning stage. Although the advantages of roundabout have been documented in the U.S., the safety benefits may vary significantly due to uniqueness of each location’s conditions and detailed design selections."br" A study conducted in Louisiana has revealed some interesting results on the safety benefits of roundabout applications from 15 locations. Minimum six years of crash information for each location were used in the analyses including not only the crash database, but also the original crash reports. Through reading the original crash reports, the research team obtained many interesting information from the narratives and collision diagram of original crash report, which proved to be very beneficial in identifying design issues and human factors relating to crash occurrences and consequences (severity)."br" The combined analysis (before-and-after and reviewing crash report) generally demonstrated that the level of success of a roundabout depends on the design details and local driving behavior. With inconsistent results in changes of total crashes before and after roundabout implementation, the analyses show that all roundabout intersections experienced a reduction in severe crashes, but increase in single-vehicle running-off-roadway crashes. The changes in total crashes varied by type of previous traffic control and design details. The significant increase of non-collision crashes (single vehicle crashes) at all roundabout intersections during the first three years of operation may result from unfamiliarity with roundabout operation, distracted drivers, large vehicles with difficulties negotiating curvature and application policy, i.e., lack of intersection lighting at rural areas. By and large, it is clear that the safety effectiveness of roundabout varied with location and design details. In order to optimize roundabout benefit at a particular location, designers must pay close attention to location geometric layout, surrounding environment, and land use. Failure to recognize the unique characteristics at each individual location may lead to unintended results.