INTERSECTION SIGHT DISTANCE

Abstract

Intersection sight distance (ISD) is intended to provide drivers at or approaching intersections with an unobstructed view of the entire intersection and of sufficient lengths of the intersecting highways to permit the approaching drivers to anticipate and avoid collisions. This requires unobstructed sight distance along each approach to the intersection, as well as across clear sight triangles between the approaches. The research obtained field data on driver behavior at intersections, particularly with respect to speed selection, acceleration and deceleration rates, gap acceptance behavior, and vehicle stopping positions. These data were used to formulate recommended geometric design policies for sight distance at intersections with no control, with Stop control on the minor road, with Yield control on the minor road, with traffic signal control, and with all-way Stop control. The recommended sight distance policies for approaches to uncontrolled and Yield-controlled intersections are based on a stopping sight distance model, modified to incorporate field results on the actual speed profiles used by drivers approaching such intersections. The recommended sight distance policies for locations at which stopped vehicles must enter or cross a major road are based on the actual gap acceptance behavior of drivers observed in the field.