Designers should strive to provide three-dimensional alignments that produce DSD as part of location planning and studies for new alignments, and in considering proposals to add new intersections and interchanges to existing highways. Designers should strive to provide three-dimensional alignments that produce DSD as part of location planning and studies for new alignments, and in considering proposals to add new intersections and interchanges to existing highways. Where DSD should be available but is not provided, the AASHTO Green Book (2) indicates that traffic-control devices, advance warning, etc., should be employed.

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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