Over the last decade, there has been a changing emphasis in geometric design away from the specification of and adherence to rigid standards, and towards an engineering decision process whereby standards are tailored to suit particular design objectives and constraints. To evaluate design options and make effective decisions, a designer requires information on the relationships between operational performance and the road geometry elements and configurations which make up the design. The paper reviews current knowledge on safety, vehicle operating costs, driver behaviour, and traffic service, as related to geometric design. Expressing accident occurrence as relative accident rates, reasonably consistent accident-width relations are available. Similar relations are available for alignment elements, but these are also dependent on alignment consistency. Free vehicle operating costs are shown to decrease with increasing alignment standard, with cars gaining relatively more from improvements to horizontal alignment and trucks gaining relatively more from improvements to vertical alignment. A consistent, but not necessarily high, standard of horizontal alignment is necessary for driver speed behaviour to accord with the side friction factor design criteria. Simulation experiments show that the construction of intermittent overtaking lanes can provide a cost-effective means of improving traffic service on two-lane roads when current and future traffic volumes do not justify a four-lane facility. (Author/TRRL)

  • Availability:
  • Supplemental Notes:
    • Proceedings of the 21st Australian Road Research Boards Regional Symposium, Darwin, North Territory, Australia, 1984.
  • Corporate Authors:


    Melbourne, Victoria  Australia 

    Southern Africa Commercial Travellers Association

    Box 828
    Cape Town,   South Africa 
  • Authors:
    • McLean, J R
  • Publication Date: 1984

Media Info

  • Features: Figures; References; Tables;
  • Pagination: p. 1-21
  • Serial:
    • On the Road
    • Volume: 7
    • Issue Number: 1
    • Publisher: Southern Africa Commercial Travellers Association

Subject/Index Terms

Filing Info

  • Accession Number: 00389179
  • Record Type: Publication
  • Source Agency: ARRB
  • ISBN: 0-86910-150-1
  • Report/Paper Numbers: HS-037 306
  • Files: ITRD, TRIS, ATRI
  • Created Date: Mar 29 1985 12:00AM