Transition Curve In Highways – Purpose-Requirements-Example

Objectives or Purpose

Transition curves are provided to serve following purposes. To provide Super Elevation in a gradual manner and to reduce the radius from infinity at a straight junction to a radius R at curved junction gradually. Transition curves also reduces the effect of sudden jerk on passengers due to the effect of centrifugal force induced on vehicles at curves.

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An ideal Transition curve should satisfy following requirements,

• The curve should be tangential at its junction points so that the radius of transition is infinity at straight junction and R at the curved junction.
• Rate of change of super-elevation is equal to the rate of change of curvature so that full super-elevation can be provided within the length of transition curve.

Spirals and clothoids are mostly adopted to provide transition curves, as suggested by design codes. Apart from these, cubic parabolic curves and lemniscates are also used as per alignment requirements. Governing parameters for setting out these curves are the acceleration of vehicles, the required super elevations, lengths available for transition and deflection angles. Empirical formulas are used to design transition curves.

Transition Curve – Straight to Curve Transformation