Transition curves are introduced at either end of a circular curve, to obtain

• gradually decrease of curvature from zero at the tangent point to the specified quantity at the junction of the transition curve with main curve
• gradual increase of super-elevation from zero at the tangent point to the specified amount at the junction of the transition curve with main curve
• gradual change of gradient from zero at the tangent point to the specified amount at the junction of the transition curve with main curve
• none of these.