U.S. Department of Transportation Federal Highway Administration

MEMORANDUM

Enclosed for each addressee is one copy of A Policy on Design Standards - Interstate System. This 2005 publication is a revision of the 1991 edition. Additional copies may be ordered from the AASHTO Bookstore at http://www.transportation.org/. A summary of the changes made in the 2005 edition is attached.

We are beginning the rulemaking process to incorporate this document into 23 CFR 625 as a design standard for projects on the Interstate System. Until such time as the rulemaking procedure is completed the Policy may be used for guidance and the 1991 version of the standard is still applicable.

Attachment

Changes in 2005 Interstate Standards (as compared with 1991 Interstate Standards)

1. Metric values have been added for all dimensions.
2. In Design Speed, the sentence specifying a separate design speed for rolling terrain has been deleted.
3. The maximum grade table has been expanded to include intermediate and higher design speeds.
4. The discussion of shoulder width in mountainous terrain has been revised.
5. The discussion of horizontal clearance to obstructions has been revised and updated.
6. The discussion of curbs has been revised and expanded.

Return to May 8, 2006 memo