Analysis of Vehicle Speeds and Speed Differentials in Curves

Horizontal curves are associated with significant numbers of fatal crashes. The safety performance of an individual curve depends on a variety of geometric factors, including radius, superelevation rate, deflection angle; vehicle speeds; and friction characteristics of the pavement. In addition, vehicle speeds in curves are influenced by curve geometry and speeds along the approach tangent. Hence, an understanding of the relationship between these various factors is important for developing an analysis framework to assess curve safety. In this paper, documented models estimate vehicle speeds at the beginning, midpoint, and end of a curve on the basis of the curve's operational and geometric characteristics. These models are applied in an analysis framework based on the concept of margin of safety, which is side friction demand subtracted from side friction supply. This method can be used to prioritize proposed treatments at curve sites and to identify points along the curve at which sliding failures are most likely to occur. The analyst must provide the key operational and geometric characteristics as well as friction characteristics of the existing pavement and proposed surface treatment.