Optimizing highway profiles for individual cost items

Abstract

According to the current practice, vertical alignment of a highway segment is usually selected by creating a profile showing the actual ground surface and selecting initial and final grades to minimize the overall cut and fill quantities. Those grades are connected together with a parabolic curve. However, in many highway construction or rehabilitation projects, the cost of cut may be substantially different from that of fill (e.g. in extremely hard soils where blasting is needed to cut the soil). In that case, an optimization process will be needed to minimize the overall cost of cut and fill rather than to minimize their quantities. This paper proposes a nonlinear optimization model to select optimum vertical curve parameters based on individual cost items of cut and fill. The parameters selected by the optimization model include the initial grade, the final grade, the station and elevation of the point of vertical curvature (PVC), and the station and elevation of the point of vertical tangency (PVT). The model is flexible to include any design constraints for particular design problems. Different application examples are provided using the Evolutionary Algorithm in Microsoft Excel’s Solver add-in. The application examples validated the model and demonstrated its advantage of minimizing the overall cost rather than minimizing the overall volume of cut and fill quantities