Assessment of horizontal curves of an existing road using reliability concepts

Horizontal curves on road are commonly analyzed under design speed point of view, where it is assumed that the maximum speed of a vehicle in a curve is the design speed. The empirical evidence has demonstrated that when the design speed is low, the operating speed tends to be higher. This happens because of an available remaining lateral (or transverse) friction for speeds over design speed. This condition is determined by a speed limit, obtained from the demand and supply equilibrium of friction of a pavement. The difference between operating and design speeds is usually considered as the margin of safety of a horizontal curve on a road. In this study, a methodology to determine the margin of safety of an existing curve is proposed. The methodology is based on the reliability theory by which reliability of operational conditions can be analyzed by using a reliability index as a margin of safety. A case study for light vehicles is evaluated to determine high impact variables over reliability, such as, macrotexture, skid resistance, curve radius, and superelevation. The results obtained in this study demonstrated that curve radius, skid resistance, and macrotexture are variables with high impact over failure probability. In constrast, superelevation has little effect on the failure probability.