When an ascending gradient of a highway meets a descending gradient, the vertical curve provided at the junction is classified as which type?

Introduction / Context:
Vertical curves connect differing longitudinal grades to provide comfort, adequate sight distance, and drainage. Their classification depends on whether the curve opens upward or downward.

Given Data / Assumptions:

• An up-grade meets a down-grade.
• No special constraints beyond standard geometric design considerations.

Concept / Approach:
When an ascending grade meets a descending grade, the curve opens upward, forming a crest—known as a summit curve. Conversely, a sag or valley curve opens downward where two descents/ascents create a low point.

Step-by-Step Solution:

Verification / Alternative check:
Graphing grade lines shows a crest at the junction, reinforcing the summit classification.

Why Other Options Are Wrong:
Valley and sag refer to downward-opening curves at low points; option (d) cannot be correct as types are mutually exclusive for a given junction.

Common Pitfalls:
Confusing the naming between crest (summit) and sag curves; overlooking which sight distance criterion applies.

Final Answer:
Summit curve