The correct answer is option 'C', a reverse curve.

Reverse Curve:
A reverse curve is a type of horizontal curve that consists of two arcs with their centers on opposite sides of the curve. In other words, it is a curve that changes direction abruptly, causing the road to reverse its curvature. This type of curve is commonly used in road design to allow for a change in direction when there are space constraints or other limitations.

Components of a Reverse Curve:
A reverse curve is composed of two separate arcs, each with its own radius and center. These arcs are connected by a tangent line, which is a straight segment of road that connects the two arcs. The tangent line helps to smooth the transition between the two arcs and ensures a continuous flow of traffic.

Purpose of a Reverse Curve:
The main purpose of a reverse curve is to allow vehicles to change direction smoothly and safely, especially in situations where a simple circular curve cannot be used due to spatial limitations. By incorporating two arcs with different radii, the reverse curve provides a more gradual change in direction, reducing the risk of accidents and improving the overall driving experience.

Characteristics of a Reverse Curve:
1. Change in Direction: A reverse curve allows for a change in direction, which can be useful in situations where a road needs to deviate from its original path to accommodate constraints such as buildings, infrastructure, or natural obstacles.

2. Continuous Flow: The tangent line connecting the two arcs ensures a continuous flow of traffic, minimizing disruptions and maintaining a smooth driving experience for motorists.

3. Safety Considerations: While reverse curves can be effective in certain situations, they can also pose challenges for drivers. It is important to provide clear signage, road markings, and adequate visibility to ensure that motorists can navigate the curve safely.

Conclusion:
A reverse curve is a type of horizontal curve that consists of two arcs with their centers on opposite sides of the curve. It is used to allow for a change in direction when space constraints or other limitations prevent the use of a simple circular curve. Implementing reverse curves requires careful consideration of safety measures and adequate signage to ensure a smooth and safe driving experience for motorists.