Model for three-dimensional highway alignment

This research develops a model to solve for the three-dimensional alignment of a highway segment. Code requirements are taken into consideration, and mechanisms for maintaining heavy vehicle speeds are embedded in the model. The model brings the highway alignment close to certain preferred points, and avoids restricted areas when required. Horizontal alignment is composed of design elements, including tangent segments, circular curves, and clothoid curves. Vertical alignment is represented by lines and vertical curves. Both alignments are highly compatible with code requirements in practice. The three-dimensional alignment is obtained through an iterative process. With each iteration, a new horizontal alignment was obtained through a slight adjustment of the current alignment. Subsequently, a corresponding vertical alignment was developed by solving a series of linear mixed integer optimization problems. The entire solution process was divided into three stages with different tasks, and the accuracies in each stage carefully set to achieve efficiency. Some computational examples are provided.