Implementing new vehicle stability-based minimum radius guidelines for simple and reverse horizontal curves: Is it cost effective?

A new and improved design approach for determining the minimum radius requirements for simple and reverse horizontal curves has been developed using advanced vehicle simulation software. The approach, which considers vehicle stability and three-dimensional (3D) alignments, produces larger radii than those presented in current geometric design guides. The larger radii (flatter curves) of the new approach provide a smoother transition between the tangent and curves of the highway and results in a reduction of the overall length of the alignment. In turn, the reduction in highway alignment results in savings in construction, maintenance, and collision costs. This paper evaluates the costs and benefits associated with implementing the new design guidelines for the minimum radius of both simple and reverse horizontal curves with intermediate tangents. Two different cases were evaluated: (1) a new alignment involving construction of the flatter horizontal curves based on the new guidelines relative to the curves of the current design guides and (2) an existing alignment for which the flatter horizontal curve is to be constructed to improve the existing alignment. The results illustrate that implementing the new minimum radius guidelines generates a more cost-effective highway alignment, in addition to satis1'ing vehicle stability requirements