ANS:B - parabolic

A rising gradient of 1 in 40 is to be connected with a falling gradient of 1 in 75 by means of a vertical equal tangent parabolic curve 400 m in length. The reduce level at the intersection point of the tangent is 26.850.

Calculate:

(1) The rate of change of grade.

(2) The reduced levels at the beginning and end tangent points. A cubic spiral is suitable to cubic parabola but latter is used mostly because of its ease in setting out. Vertical curves are provided to negotiate the gradient of the two straights. Parabola is most suitable shape for vertical curves since it provides a uniform rate of change of gradient and smooth riding condition. In highway engineering, we deal with two type of vertical curves summit and valley.

IRC CLEARLY have defined the ideal vertical curves for summit it is circular and for valley it is cubic. Ideal vertical curve is circular if sight distance available throughout the length of curve is constant it possible only in case of Joining one Gradient.

In this case, two gradient are Joint by curve therefore sight distance is not constant throughout the length of curve so we provide Simple Parabolic curve. Ideal vertical curve is circular if sight distance available throughout the length of curve is constant it possible only in case of Joining one Gradient. In this case, two gradient are Joint by curve therefore sight distance is not constant throughout the length of curve so we provide Simple Parabolic curve. Because the parabolic curve can be either sag or summit curve, in both the cases parabolic curve provides the best curve to provide maximum comfort to the passengers pr driver.