AASHTO refers to DSD as "desirable" and "appropriate." Providing DSD is clearly recommended as an element of a high-quality alignment. AASHTO refers to DSD as "desirable" and "appropriate." Providing DSD is clearly recommended as an element of a high-quality alignment. The AASHTO Green Book (2) does not contain language mandating the provision of DSD. This is consistent with the view that DSD, while desirable, is not considered as essential as other sight distance requirements such as SSD or ISD.

From A Guide for Achieving Flexibility in Highway Design, 2004, by the American Association of State Highway and Transportation Officials, Washington, D.C. Used by permission. AASHTO publications may be purchased from that organization's bookstore at 1-800-231-3475 or online at http://bookstore.transportation.org.

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