An evolutionary model for simultaneously optimizing three-dimensional highway alignments

Optimizing highway alignments is a very complex engineering problem. The factors that should be considered in the design process are complex and interrelated. Although several mathematical models have been developed to solve the alignment optimization problem, most of them emphasize either horizontal or vertical alignments, and only yield a suboptimal solution to the problem. Models for simultaneously optimizing three-dimensional alignments are rare in the literature and their capabilities are quite limited. In this paper, an evolutionary model (a search algorithm that imitates the natural evolution process) for solving three-dimensional alignment optimization problems is developed. It overcomes some drawbacks in existing models. The cost components and design constraints embedded in it can be comprehensive. The proposed algorithm can optimize complex, comprehensive, and non-differentiable objective function. The model can also exploit detailed geographical information for highway analysis. The resulting alignments are smooth everywhere and can have backward bends (i.e., backtracking) to better fit terrain and land-use patterns. A numerical example is presented to illustrate the proposed model and the performance of the solution algorithm. (C) 2002 Elsevier Science Ltd. All rights reserved.