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Determination of SSD values is highly dependent on the selected design speed. Flexibility within the Green Book (2) is thus primarily provided by the ranges of design speeds afforded designers.
Determination of SSD values is highly dependent on the selected design speed. Flexibility within the Green Book (2) is thus primarily provided by the ranges of design speeds afforded designers.
The 2001 edition of the Green Book (2) incorporates research from NCHRP Report 400: Determination of Stopping Sight Distances (20). SSD values and associated vertical curve design requirements are less stringent than in previous editions for a given design speed. This may result in some additional flexibility to designers faced with reconstruction of roads built under previous guidelines.
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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