Superelevation Design, Definitions (2024)

This Article Covers What Is Superelevation, Super Elevation Formula, Design Of Super-elevation And How It Attained One By One.

What Is Superelevation

The amount by which the outer edge of a curve on a road or railway banked above the inner edge non superelevation.

Superelevation is the banking of a roadway along a horizontal curve so motorists can safely and comfortably maneuver the curve at reasonable speeds

When being applied to the road need to take into account

  • Safety
  • Comfort
  • Appearance
  • Design speed
  • Tendency for slow vehicles to track towards centre
  • Difference between inner and outer formation levels
  • Stability of high laden vehicles
  • Length of road to introduce superelevation
  • Provision for drainage

Design Of Superelevation

For fast moving vehicles, providing higher superelevation without considering coefficient of friction is safe, i.e. centrifugal force is fully counteracted by the weight of the vehicle or superelevation.

For slow moving vehicles, providing lower super-elevation considering coefficient of friction is safe, i.e.centrifugal force is counteracted by superelevation and coefficient of friction.

Maximum Superelevation

  • Max range from flat to mountainous of 0.06 – 0.12 respectively but most authorities limit to 0.10
  • In urban areas limit max values to 0.04-0.05 Minimum Super-elevation
  • Should be elevated to at least the cross-fall on straights i.e 3% (0.03)

Attainment Of Super-Elevation

Elimination of the crown of the cambered section by:

  • Rotating the outer edge about the crown
  • Shifting the position of the crown

Rotation of the pavement cross section to attain full super elevation by:

  • There are two methods of attaining super-elevation by rotating the pavement
  • Rotation about the center line
  • Rotation about the inner edge

Radius of Horizontal Curve

The radius of the horizontal curve is an important design aspect of the geometric design. The maximum comfortable speed on a horizontal curve depends on the radius of the curve.

Although it possible to design the curve with maximum super-elevation and coefficient of friction, it is not desirable because re-alignment would required if the design speed increased in future.

Therefore, a ruling minimum radius Rruling can derived by assuming maximum super-elevation and coefficient of friction.

Rruling = V2/g(e + f )

Ideally, the radius of the curve should be higher than Rruling. However, very large curves are also not desirable. Setting out large curves in the field becomes difficult. In addition, it also enhances driving strain.

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