SIGHT DISTANCE MODEL FOR UNSYMMETRICAL CREST CURVES (WITH DISCUSSION AND CLOSURE)

In the AASHTO geometric design policy, the need for using unsymmetrical vertical curves because of clearance restrictions and other design controls is pointed out. Formulas for laying out these curves are presented in the highway engineering literature. However, no relationships are available concerning sight distance characteristics on these curves. A sight distance model for unsymmetrical crest curves has been developed to relate the available sight distance to the curve parameters, driver and object heights, and their locations along the curve. These relationships are used in a procedure for determining the available minimum sight distance. The model is used to explore the distinct features of sight distance profiles on unsymmetrical crest curves. To facilitate practical use, the model is used to establish design length requirements of unsymmetrical crest curves based on the stopping, decision, and passing sight distance needs presented by recent innovative approaches and by AASHTO. The model should prove useful in the design and safety evaluation of critical highway locations.

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  • This paper appears in Transportation Research Record No. 1303, Geometric Design Considerations 1991. Distribution, posting, or copying of this PDF is strictly prohibited without written permission of the Transportation Research Board of the National Academy of Sciences. Unless otherwise indicated, all materials in this PDF are copyrighted by the National Academy of Sciences. Copyright © National Academy of Sciences. All rights reserved
• Authors:
  • Easa, Said M
• Discussers:
  • Guell, David L
• Publication Date: 1991

Media Info

• Features: Figures; References; Tables;
• Pagination: p. 39-50
• Monograph Title: Geometric design considerations, 1991
• Serial:
  • Transportation Research Record
  • Issue Number: 1303
  • Publisher: Transportation Research Board
  • ISSN: 0361-1981

Subject/Index Terms

• TRT Terms: Curves (Geometry); Geometric design; Highway curves; Mathematical models; Passing zones; Sight distance
• Identifier Terms: American Association of State Highway and Transportation Officials
• Uncontrolled Terms: Vertical curvature
• Old TRIS Terms: Crest; Sight distance, minimum non passing; Unsymmetrical
• Subject Areas: Design; Highways; I20: Design and Planning of Transport Infrastructure;

Filing Info

• Accession Number: 00616588
• Record Type: Publication
• ISBN: 030905110X
• Files: TRIS, TRB
• Created Date: Nov 30 1991 12:00AM