Abstract
Sight distance is a key element in highway geometric design. Existing models for evaluating sight distance are applicable only to two-dimensional (213), separate horizontal, and vertical alignments or simple elements of these separate alignments (vertical curve, horizontal curve). A new model using global positioning system (GPS) data is presented for determining the available sight distance on 3D combined horizontal and vertical alignments. Piecewise parametric equations in the form of cubic B-splines are used to represent the highway surface and sight obstructions, including tangents (grades), horizontal curves, and vertical curves. The available sight distance is found analytically by examining the intersection between the sight line and the elements representing the highway surface and sight obstructions. A profile of available sight distance can be established and used to evaluate sight-distance deficiency. Application of the new model is illustrated using actual GPS data for highway K-177 in Kansas (United States). The model has been tested and verified on most of the highways in Kansas. Software has been developed and can be used for determining the available sight distance on any highway for which GPS data are available.
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