Why are reverse curves seldom used in highway or railway alignments?

Reverse curves are seldom used in highway or railway alignments primarily due to the abrupt direction changes they create. In the context of transportation engineering, the design of roadways and railways prioritizes smooth transitions to enhance safety and comfort for users. When a curve reverses direction sharply, it can lead to challenges in maintaining speed and stability for vehicles or trains traveling along the path.

Abrupt direction changes can cause drivers or operators to experience discomfort, as they must quickly adjust their handling to navigate these shifts. Additionally, such design features may interfere with sightlines for operators, increasing the risk of accidents or collisions, as they may not have sufficient visibility to anticipate the upcoming change in direction.

While the other factors—such as cost, material requirements, and visibility—may influence design decisions, the key issue with reverse curves revolves around the smoothness of the trajectory and the safety implications of sudden directional changes. Therefore, engineers typically seek more gradual curves or tangents to ensure both safety and efficiency on highways and railways.