HORIZONTAL CURVE DESIGN: AN EXERCISE IN COMFORT AND APPEARANCE

AASHTO's 1990 "A Policy on Geometric Design of Highways and Streets" contains information on procedures for three superelevation designs: rural highways and high-speed urban streets, low-speed urban streets, and curvature of turning roadways and curvature at intersections. The history of the horizontal curve design procedures through the published policies (1940 to 1990) is reviewed, the findings from the literature on key issues are presented, and additional research needs on side friction factors and transition length determination are discussed. The side friction factors used in high-speed and low-speed design were determined by using vehicle occupant comfort as the selection criterion. This criterion assumes that drivers limit their speed on curves to ensure comfort and that discomfort is directly related to the unbalanced side friction. Several concerns or issues accompany these assumptions. For example, the speed at which discomfort (or side pitch) first becomes noticeable may be slower than necessary for comfort or safety, and the level of discomfort felt by a driver may not be solely related to side friction only. These assumptions also do not directly consider vehicle characteristics or constant safety factors over the range of design speeds. Transition length determination for high-speed and intersection design is based on appearance and comfort. The criterion was developed to avoid an appearance that results from too rapid a change in superelevation. For low-speed design, a change in acceleration over the change in time factor, known as C, is used to determine superelevation runoff. High-speed design includes factors that are to be used to determine runoff lengths for roads with more than two lanes. Low-speed design does not include similar factors that adjust for wider pavements; however, it does include a method for adjusting runoff length for radii larger than the minimum that the high-speed design procedure does not include. Three research areas were identified on the basis of the present findings: (a) selection of side friction factors, (b) determination of transition lengths, and (c) evaluation of the need for and basis of the three different design procedures (high speed, low speed, and curvature at intersections). Research is needed in these areas because current practice is largely based on limited empirical data and existing practice without supporting material. Efforts to address these issues would require substantial funds.

• Record URL:
  http://onlinepubs.trb.org/Onlinepubs/trr/1994/1445/1445-005.pdf
• Record URL:
  https://scholar.google.com/scholar_lookup?title=HORIZONTAL+CURVE+DESIGN%3A+AN+EXERCISE+IN+COMFORT+AND+APPEARANCE&author=K.+Fitzpatrick&publication_year=1994
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• Supplemental Notes:
  • This paper appears in Transportation Research Record No. 1445, Cross Section and Alinement Design Issues. 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:
  • Fitzpatrick, Kay
• Publication Date: 1994

Language

• English

Media Info

• Features: Figures; References; Tables;
• Pagination: p. 47-53
• Monograph Title: Cross section and alinement design issues
• Serial:
  • Transportation Research Record
  • Issue Number: 1445
  • Publisher: Transportation Research Board
  • ISSN: 0361-1981

Subject/Index Terms

• TRT Terms: Comfort; Curves (Geometry); Friction factor; Geometric design; Guides to the literature; High speed ground transportation; High speed vehicles; Highway design; History; Literature reviews; Research; Speed; Superelevation; Traffic speed
• Uncontrolled Terms: Horizontal curvature; Low speed; Side friction factors
• Old TRIS Terms: Curvature at intersections; Transition length
• Subject Areas: Design; Highways; History; Railroads; Research; I20: Design and Planning of Transport Infrastructure;

Filing Info

• Accession Number: 00675329
• Record Type: Publication
• ISBN: 0309060516
• Files: TRIS, TRB, ATRI
• Created Date: Mar 20 1995 12:00AM