How is sight distance affected by horizontal curves?

On horizontal curves, sight obstructions (cut slopes, barriers, buildings) on the inside may limit sight distance. Required clearance m from centerline to obstruction: m = R(1 - cos(delta/2)) where delta = curve angle for sight distance S. For S < curve length: m = R(1 - cos(28.65*S/R)). Design ensures adequate clearance for stopping sight distance. If obstruction cannot be moved, options include reducing design speed, widening shoulders, or cutting into slopes. Sight triangles at intersections on curves require special attention.