Generating Sight Distance Profiles for Arbitrary Horizontal Alignments with Non-uniform Lateral Clearance

David J. Lovell, Jyh-Cherng Jong, and Peter C. Chang

Proceedings of the 2nd International Symposium on Highway Geometric Design, Mainz, Germany, June 2000, pp. 422-433.

ABSTRACT

Most of the research to date on sight distance measurements from horizontal alignment data has focused on the development of closed-form solutions for various specific cases of sequences of curves, such as a tangent followed by a circular curve or a circular curve and Euler spiral in tandem. Furthermore, it is typically assumed that the sight distance is constrained by a specific uniform lateral clearance along the alignment, or in some cases, by a single specific sight distance obstruction, such as a building. Recently, methods have been proposed to address the question of sight distance measurement along an arbitrary horizontal alignment, but still with the uniform lateral clearance assumption. In this paper, this assumption is relaxed, and an algorithm is developed for determining the sight distance profile along an arbitrary horizontal alignment where the lateral clearance can be an arbitrary continuous and non-negative function of the distance along the roadway centerline. Furthermore, this continuous boundary can be perturbed around a number of discrete sight obstructions using methods of curve-fitting. The resulting smooth obstruction curve can then be used to calculate more accurate sight distance profiles, employing methods described in earlier works.