Some 25 years ago, horizontal alignment design standards in both Australia and Canada closely resembled those recommended by the American Association of State Highway Officials (AASHO). Subsequent developments in curve design in both countries have resulted in a divergence in design practices. These developments, and the reasons for them, are reviewed. Developments in Canada have been in response to concerns with the very low levels of friction provided by icy roads and have involved reductions to design side friction factors for high speed alignments and changes to superelevation practice. Road surface friction is less of a problem in Australia and the major change has been the development of operating speed approaches to designing lower speed alignments with a view to providing satisfactory low cost alignments in difficult terrain. However, when allowance is made for the different design speed concepts, the actual differences in practice are not as great as would appear from a cursory comparison of the specified standards.
Samenvatting