Rollover Propensity of Heavy Vehicles at Roundabouts: Case Study on High- and Low-Speed Roads

In Indiana, roundabout construction recently commenced on high-speed roadways (i.e., with posted speed limits of 50 mph or higher), many carrying significant truck traffic. Studies show that heavy vehicle rollovers may be an issue at roundabouts. A case study compared the safety-related behavior of truck drivers at roundabouts on low- and high-speed roads. The rollover model is more suitable for truck trailers than previous models used for design considerations because it accounts for the complex paths and vehicle tilt of semitrailers and other heavy vehicles. The model was used to determine the difference between the critical rollover speed determined from the model and the observed vehicle speed. The proximity to rollover in the roundabout circulating lane was found to be different on low- and high-speed roads. However, this difference could not be explained by actual driver approach speeds. Drivers on the high-speed approach began decelerating earlier than those on the low-speed approach, and their deceleration rates were similar. In addition, vehicle speeds on the high-speed approach were only 1 mph faster than those on the low-speed approach close to the roundabout. The average minimum proximity to rollover on the circulatory roadway was about 3 mph slower on the low-speed, one-lane roundabout than on the high-speed, two-lane roundabout, and this difference might have been the main reason for higher risk of circulatory rollover in the one-lane roundabout.