What is a horizontal circular curve defined as?

A horizontal circular curve is defined as a circular arc that connects two straight lines, which are known as tangents. This definition captures the essence of what a horizontal circular curve is used for in civil engineering and road design; it facilitates smooth transitions between straight sections of roadway. The arc is designed to provide a consistent radius, allowing vehicles to navigate between these sections without sharp turns, which enhances safety and driving comfort.

In civil engineering, it is crucial to ensure that the pathway curves seamlessly, as abrupt changes in direction can lead to accidents or strain on the vehicle. Hence, the definition precisely indicates that a horizontal circular curve is characterized by its connection between two straight lines, maintaining a specific radius throughout, which optimizes travel on highways and roads.

The other options do not accurately describe the fundamental characteristics of a horizontal circular curve. A straight line connecting two endpoints does not represent a curve at all. A circular pathway intersecting at a right angle implies specific geometric relationship that is not a defining feature of horizontal curves. Lastly, a curve that only changes direction lacks the requisite circular nature and does not communicate the specifics of a circular arc, which defines the concept of a horizontal circular curve in the context of civil engineering design and practice.