superelevation

Superelevation is the practice of tilting a roadway around a curve so that the outer edge is higher than the inner edge. This banking helps counteract the lateral inertial forces that act on vehicles as they traverse a curve, reducing reliance on tire friction and improving stability, passenger comfort, and safety. It is applied to curved sections of highways and rail alignments and is designed in combination with the cross-slope to maintain drainage.

In practice, superelevation is implemented by raising the outer edge of the pavement relative to the inner edge, while the pavement cross-section also includes a cross-slope to shed water. The amount of raise typically increases along the curve from zero at tangent points to a maximum at or near the curve’s apex, with a transition zone that avoids abrupt changes. The transition length depends on design speed, curve radius, and local standards.

Design considerations include vehicle speed and mix, curve radius, pavement type, climate, drainage, and use of constant or variable superelevation along the curve. Maximum usable superelevation varies by region and standard, but commonly ranges from about 2% to 6% for many highways, with higher values (up to 8%–10% in some areas) permitted on high-speed or arid-region highways. Urban streets often employ lower values or none at all. Transition lengths and the interaction with cross-slope and drainage are key factors in achieving a safe, smooth design.

Standards and practices vary by country and authority, but superelevation remains a core element of curve design to balance safety, comfort, and drainage while accommodating climate and pavement constraints.