Adopting the Performance Margin in Horizontal Curve Design

A vehicle negotiating a curve experiences a centripetal force that is partially supplied by the tire–pavement friction. The American Association of State Highway and Transportation Officials’ design handbook, A Policy on Geometric Design of Highways and Streets (“Green Book”), dictates the design of horizontal curve segments according to the side friction (demand) factor, which is a fraction of the available friction used during a maneuver. However, the Green Book casts the side friction factor not as a measure of tire–pavement friction but as a measure of lateral acceleration. In this way, the Green Book conflates these independent concepts (tire–pavement friction versus lateral acceleration). It is shown in this work that keeping these curve design parameters independent has meaningful benefits. A rigorous mathematical clarification of the differences among the side friction (demand) factor, lateral acceleration, and coefficient of friction is developed. It is shown that changing the coefficient of friction affects the side friction factor, but the opposite is not necessarily true. An alternate metric is proposed, the performance margin (PM), that has several advantages for assessing friction margins. Currently, horizontal curves are designed only with a lateral friction reserve. Excluding longitudinal dynamics may not be realistic given the manner in which drivers react in limit handling maneuvers. The PM accounts for both bidirectional dynamics and road geometry, and highlights regions where the Green Book’s standards are inconsistent with vehicle performance capabilities. The work concludes by posing recommendations aimed at implementing the PM in future Green Book editions.

• Record URL:
  • https://doi.org/10.1177/03611981241229090
• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/issn/03611981
• Supplemental Notes:
  • Every effort is made to use terminology and nomenclature as described by SAE J670 (43). Without loss of generalization, the concepts in this work are developed for a left turn.© The Author(s) 2024.
• Authors:
  • Jaisohn Kim, Troy
  • 0000-0003-2118-0875
  • Ferris, John B
• Publication Date: 2024-9

Language

• English

Media Info

• Media Type: Web
• Features: References;
• Pagination: pp 267-280
• Serial:
  • Transportation Research Record: Journal of the Transportation Research Board
  • Volume: 2678
  • Issue Number: 9
  • Publisher: Sage Publications, Incorporated
  • ISSN: 0361-1981
  • EISSN: 2169-4052
  • Serial URL: http://journals.sagepub.com/home/trr

Subject/Index Terms

• TRT Terms: Coefficient of friction; Friction; Friction factor; Highway curves; Highway design; Lateral acceleration; Rolling contact
• Identifier Terms: AASHTO Green Book
• Subject Areas: Design; Highways;

Filing Info

• Accession Number: 01907942
• Record Type: Publication
• Files: TRIS, TRB
• Created Date: Feb 12 2024 6:20PM