Rotation of the Carriageway (Superelevation) in Germany and Austria – State of the Art

Abstract

The change in carriageway cross slope (rotation; torsion; superelevation) usually takes place within the transition curve, regardless of the reference line around which the carriageway surface is rotated. If there is no transition curve, half of the rotation is carried out before and half after the point where the two elements meet. In the exceptional case that the rotation takes place on a straight line, it should be positioned either at the beginning or at the end of the straight line. Rotation on structures should be avoided wherever possible (RAL, 2012). Transition curves are essential on all motorways, with one key exception: if the angle change in the curve is minimal (γ is less than 10 gon or 9°, indicating a flat curve), it may be impractical to incorporate a transition curve, followed by a circular curve, and then another transition curve. In such situations, the minimum curve length (L_min) should be at least 300 meters (RAA, 2008). As a rule, transition curves should be used between straight lines and circular arcs as well as between circular arcs. In justified exceptional cases, however, transition curves can be omitted if the differences in curvature between the two elements are very small. Such a waiver is possible for the transition from a straight line to a radius of R ≥ 1,000 m and for a spiral line between two radii of R ≥ 2,000 m (RAL, 2012).