Approximate Perspective Design of Roads

Abstract

Coordination of horizontal and vertical alignments is an important principle in road geometric design, and it should begin with preliminary design. Perspective drawings and sketches are considered to be effective means for evaluating this coordination. In the present paper, an approximate method is developed for the quick and adequately accurate drawing of the perspective of a road, and a relevant example is given. The method is based on the use of vanishing points and the properties of an equal-tangent parabola. It is assumed that the spatial curve of the centerline of a road element—defined as a road section along which the horizontal and vertical curvatures are constant—is an equal-tangent parabola. The proposed method does not substitute computer-aided drawing of the perspective, which is essential during the detailed design stage. It is nevertheless judged to be useful and more appropriate during the preliminary design stage, for it allows an engineer, designer, or researcher to reliably trace the perspective view of various horizontal and vertical alignment combinations and to obtain the desired coordination.