Talk:233.2 At-Grade Intersections with Stop and Yield Control

The minimum sight distance for at-grade intersections, entrances, and median openings, measured along the centerline of the main road, is equal to the Entering Sight Distance based on the operating speed of the main road. This distance is based on a 3.5 ft. (1070 mm) height of eye and 3.5 ft. (1070 mm) height of object. The minimum sight distance at all grade intersections measured along the minor road, is the stopping sight distance based on the operating speed of the minor road.

IS THE HEIGHT OF OBJECT REALLY 3.5? The Stopping sight distance height of object is 2, under Driveway and entrances, the entering sight distance is 2.

If this is the case for the 3.5' height of object, the vertical curves will have to be manually calculated instead of using geopak. Also, if this is the case, the chart (listing minimum SSD, minimum entering sight distance and design sight distance) will have to clearly define that the entrance and the SSD distances are calculated differently from one another (one using the 2' object height and the other using 3.5').

Sam Masters: A review of the "Green Book" reveals the height of the object is 2.0 ft. when computing or measuring stopping sight distance. 233.2 has beeen changed to reflect this information. Thanks for the comment.

The height of object for Entering Sight Distance should be 3.5 feet. See the 2004 "Green Book" pages 653-654. Note the height of driver's eye is also 3.5 feet for passenger cars and 7.6 feet for trucks. --Martik2 12:59, 29 January 2009 (CST)