Automated Calculation of Sight Distance from Horizontal Geometry

Abstract

This paper describes a method for automatic calculation of sight distance, subject only to constraints of horizontal geometry, along an arbitrary alignment of tangent sections, circular curves, and spiral transition curves. A parametric representation is used to describe the alignment and its tangent and normal vectors at all points. From this information, other parametric forms are derived that describe the curve along the center of the traveled lane and the lateral obstruction curve. Finally, an automatic method to determine sight distance is described, which is analogous to the manual “graphical method” often employed in practice. An example alignment is considered for demonstration purposes. The method is accurate, efficient, and consistent with manual calculations. It might be used for situations where detailed information about possible sight distance obstructions is not available, such as planning, preliminary design, or to support passing behavior modules of microscopic simulation models.