SUPERELEVATION RATES AT RURAL HIGHWAY INTERSECTIONS. FINAL REPORT

Standard superelevation rates on rural highways may be as high as 12% depending on the curve radius and design speed. One common design situation in rural areas occurs when a cross street intersects the main highway at a curved, superelevation section. In these cases, the highway designer may reduce mainline superelevation to facilitate vehicles turning onto the mainline from the intersecting cross street. This research investigates the relative impact of these reduced superelevation rates on large vehicles (e.g., trucks, tractor semi-trailer combinations, etc.), and includes 1) a review of accident records at similar sites in California, and 2) a dynamic analysis of large vehicle dynamics at alternate section curve designs. Results suggest that the practice of nominal reductions of superelevation rates on section curves accomplishes the desired goal of increasing the margins of safety on the cross street while producing only minor reductions to the failure speeds of vehicles traversing the rural highway.