INTERSECTION SIGHT DISTANCE

This paper describes the development of recommended revisions to the intersection sight distance policy of the 1994 AASHTO Green Book, A Policy on Geometric Design of Highways and Streets. The conclusions are based on field observations of driver behavior at a variety of selected at-grade intersections, including those with no control, with minor-road Yield control, and with minor-road Stop control. Current AASHTO intersection sight distance procedures are intended to provide adequate sight distance at intersections to promote safe and efficient traffic operations. The recommended revisions to the AASHTO Green Book developed during this research were presented to the AASHTO Task Force on Geometric Design at the Summer 1996 meeting as the first step towards possible AASHTO adoption. Those recommendations were reordered from the Case I through Case V format of the 1994 Green Book because the recommended sight distance for Yield-controlled intersections, currently Case II, depends in part on the recommended model for Stop-controlled intersections, currently Case III. Recommended sight distance policies are presented for the following situations: Case A. Intersections with no control; Case B. Intersections with Stop control on the minor road; Case B1. Left turns from the minor road; Case B2. Right turns from the minor road; Case B3. Crossing maneuver from the minor road; Case C. Intersections with Yield control on the minor road; Case C1. Crossing maneuver from the minor road; Case C2. Left or right turns from the minor road; Case D. Intersections with traffic signal control; Case E. Intersections with all-way Stop control; Case F. Left turns from a major road.