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

• A. gradually decrease of curvature from zero at the tangent point to the specified quantity at the junction of the transition curve with main curve
• B. 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
• C. gradual change of gradient from zero at the tangent point to the specified amount at the junction of the transition curve with main curve
• D. none of these.