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)

Sam Masters: After further discussion and review of the "Green Book" (pages 113, 653 & 654), clarification has been added to the table in 233.2.1.1. Stopping Sight Distance is based on an eye height of 3.5 ft. and an object height of 2.0 ft. Entering Sight Distance (for cars) is based on an eye height of 3.5 ft. and an object height of 3.5 ft. (for trucks the height of eye becomes 7.6 ft.).

Link Correction

Under 233.2.5 is the following:

Signing and striping considerations - It is important to clearly mark and sign the intersection. Refer to EPG 903.13.25 for signing. - If the crossroad is a city or county road, it is recommended to install the following left turn lane sign at the beginning of the offset left taper:

EPG 903.13.25 is a link and takes you to 903.17 page in which you can scroll down to 903.17.25 which is the correct area to be looking at. Please correct the link text to be the section number that it takes you to. Thank you.

Keith L. Smith: Sounds like a great idea. The link has been updated. Thanks for helping to keep the EPG up-to-date!