Curves

Curves are the bends provided in Highways and Railways to change the direction of the route.

Why Curves are provided?

Before answering that, choose the Case…

Which Case to Choose and Why?

The curves are provided to

• Maintain the speed of the vehicle.
• Avoid accidents or safe turning.
• Provide comfort to the passengers.

Curves

• Curves are provided whenever a road changes its direction from right to left or left to right and changes its alignment from up to down or down to up.
• Curves enables the vehicle to pass from one straight road to another, so that the change of direction at the intersection may be gradual.

Which parameter helps us in differentiating big and small curves?

A curve consists of two or more arcs with different radii is called compound curve.

Reverse Curves

• A curve consists of two arcs bending in opposite directions. Their center lie on the opposite side of curve is called reverse curve.

Transition Curve
• A curve of varying radius is known as transition curve.
• It is also called spiral curve or easement curve.
• A transition curve is provided on both ends of a circular curve, mostly in railways to minimize the superelevation and to ensure the safe turning of trains.

Notation in Circular Curves

PI: Point of Intersection of two tangents; also called vertex, V.

PC: Point of commencement of curve; start point of the curve.

PT: Point of tangency; end point of the curve.

Note that the radii at PC and PT are perpendicular to the back tangent and forward tangent, respectively.

The distance from PC to PI and from PI to PT

is called the tangent distance, T.

The line connecting the PC and PT is the long chord LC.

Example :Two tangents AB and BC intersect at a point B at 150.5 m chainage. Calculate all the
necessary data for setting out a circular curve of 100 m radius and deflection angle
30° by the method of offsets from the long chord.

Example : Two tangents intersect at chainage 1250 m. The angle of intersect is 150°. Calculate
all necessary for setting out a curve of radius 50 m by deflection angle method. The
peg intervals may be taken as 20m. Prepare setting out table.