Understanding Reverse Curves

A reverse curve is a specific type of curve used in the design of roads, railways, and canals. It is characterized by two circular curves of opposite curvature joined together. This means the curve first bends in one direction and then immediately bends in the opposite direction, forming an 'S' shape.

Reverse Curve Classification

Curves in civil engineering design are broadly classified based on the plane in which they lie:

• Horizontal Curves: These curves are used to change the alignment or direction of a route in the horizontal plane. When you look at a road or railway from above, a horizontal curve looks like a bend to the left or right.
• Vertical Curves: These curves are used to provide a smooth transition between different gradients in the vertical plane. When you look at a road or railway from the side, a vertical curve looks like a hump (summit curve) or a dip (sag curve).

A reverse curve facilitates a change in horizontal direction, as it involves curves bending left and right (or vice versa) on a horizontal plane to navigate obstacles or fit topography. Since a reverse curve is defined by its change in horizontal alignment, it falls under the category of horizontal curves.

Comparing Reverse Curves to Other Options

• Vertical curve: Vertical curves (like sag and summit curves) deal with changes in elevation or gradient, not horizontal direction. A reverse curve deals with changing horizontal direction.
• Sag curve: A sag curve is a specific type of vertical curve used in dips or valleys where the grade changes from a descending slope to an ascending slope. This is different from a reverse curve.
• Summit curve: A summit curve is a specific type of vertical curve used on crests or humps where the grade changes from an ascending slope to a descending slope. This is also different from a reverse curve.

Therefore, a reverse curve is fundamentally a type of horizontal curve.