Low-Clearance Truck’s Vertical Requirements at Roundabouts

While roundabouts have already been proven to be an effective intersection treatment, there are many instances where low-clearance vehicles have problems using roundabouts.Low-clearance vehicles, such as lowboy trailer trucks, have problems, damaging the curbs and truck aprons at roundabouts when there is not sufficient ground clearance.This area has been generally neglected by designers and U.S. states.The latest roundabout manual has guidelines available to design various features of the roundabouts, but they are not specific for low-clearance vehicles.While some previous studies have identified roundabout locations with ground-clearance problems for lowboy trailers that have truck-apron heights that are greater than three inches, no published information is available about truck-apron heights based on three-dimensional analyses.This study addresses the ground-clearance problems for low-clearance vehicles at roundabouts by proposing a procedure where truck-apron heights, truck-apron slope, circulatory roadway slope, and approach roadway slope are analyzed to determine the optimum design measurements for a roundabout's vertical profile in order to accommodate low-clearance vehicles without terrain conflict.The study procedure was demonstrated on standard single-lane roundabouts and double-lane roundabouts designed according to latest roundabout guide, and recommendations were provided for truck-apron heights and the grade for various features of the roundabouts.This research can guide transportation planners and decision makers when determining the optimum roundabout vertical-profile design when low-clearance vehicles are expected.The study uses TORUS software to design roundabouts, and the AUTOTURN and AUTOTURN Pro 3D software for generating two-dimensional and three-dimensional vehicle simulations as well as for conducting three-dimensional vehicle-clearance analysis.