What does "horizontal alignment" refer to in highway design?

In highway design, the term "horizontal alignment" refers specifically to the layout of the roadway as it changes direction, including both left and right curves. This aspect of design is crucial because it impacts how vehicles navigate the road, affecting safety, speed, and overall flow of traffic. Proper horizontal alignment ensures that the curves are gentle enough to maintain safe speeds while still allowing for effective vehicle maneuverability.

When considering highway design, the horizontal alignment must account for factors such as the radius of curves, superelevation (banking of curves), and sight distance to provide drivers with adequate visibility and control as they navigate through curved sections. Ensuring proper horizontal alignment helps prevent accidents and provides a smoother driving experience.

The other options, while relevant to various aspects of roadway design, do not encapsulate the definition of "horizontal alignment." Width of lanes pertains to lane design, elevation addresses vertical alignment, and location of traffic signs relates to road signage and communication with drivers. Therefore, the focus on the curvature of the roadway makes the choice regarding how the roadway curves left or right the correct interpretation of horizontal alignment.