Concept: Sight distance available from a point is the actual distance along the road surface, over which a driver from a specified height above the carriageway has visibility of stationary or moving objects. Three sight distance situations are considered for design:
● Stopping sight distance (SSD) or the absolute minimum sight distance ● Intermediate sight distance (ISD) is defined as twice SSD ● Overtaking sight distance (OSD) for safe overtaking operation ● Headlight sight distance is the distance visible to a driver during night driving under the illumination of headlights ● Safe sight distance to enter into an intersection