Intersection sight distance is the adequate sight distance to be provided at two-way stop controlled intersection. Current AASHTO policy provides an equation and charts for the required at-grade intersection sight distance so that a driver on the minor road can depart (crossing, turning left, or turning right) safely, even though an approaching vehicle on the major road comes into view as the stopped vehicle begins to depart. The AASHTO model is based on two assumptions: (a) both minor and major roads are assumed to be straight without any vertical or horizontal curvature and (b) the intersection angle is assumed to be 90°. In many practical situations, however, we have to check sight distance for an existing three-dimensional (3D) highway alignment where vertical and horizontal curves overlap at the intersection. This paper provides a new analytical model for intersection sight distance on 3D highway alignments, which allows the major road to have vertical and horizontal curves with any intersection angle. Practical graphical aids are developed to determine the available intersection sight distance for different geometric alignment variables (e.g., radius of horizontal curve, lane width, number of lanes, length and grades of vertical curve). The methodology is illustrated using several numerical examples.

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Conference Canadian Society for Civil Engineering - 30th Annual Conference: 2002 Chellenges Ahead
Dabbour, E. (Essam), Easa, S. (Said), Hassan, Y, & Halim, A.O. (2002). Analytical model for intersection sight distance on 3-D highway alignments. In Proceedings, Annual Conference - Canadian Society for Civil Engineering (pp. 2491–2502).