Purpose of horizontal curves – operational and safety benefits Why are horizontal curves provided on highways, beyond the basic need to change direction?

Introduction / Context:
Horizontal curves are essential alignment elements that provide directional change smoothly. They also serve human factors objectives, improving safety and driver performance on long tangents.

Given Data / Assumptions:

• Highway environment with potentially long, straight sections.
• Drivers may experience monotony and speed creep on very long tangents.

Concept / Approach:
Long unbroken tangents can induce monotony, leading to reduced vigilance and creeping speeds. Introducing suitable curves regulates operating speeds, provides visual stimulation, and reduces mental strain, thereby lowering crash risk without compromising capacity.

Step-by-Step Solution:
Recognize human-factor benefits: curves break visual monotony → better vigilance.Speed management: curvature naturally moderates speeds → discourages overspeeding.Workload balance: curves and varying scenery reduce mental fatigue.Hence, all listed reasons apply.

Verification / Alternative check:
Operational studies link extremely long tangents to speed dispersion and inattention; context-appropriate curvature can mitigate these effects.

Why Other Options Are Wrong:
Each individual reason is valid; none is incorrect.

Common Pitfalls:
Overusing sharp curves for speed control rather than employing context-sensitive design; failing to coordinate with sight distance and superelevation.

Final Answer:
all the above