Highway / railway curves — the “Point of Curve (PC)” of a simple circular curve refers to which location on the alignment? Choose the most accurate definition.

Introduction / Context:
On a simple circular curve, key points define geometry and setting-out: PI (point of intersection), PC (point of curve), and PT (point of tangency). Understanding these labels is crucial for field layout and for interpreting design drawings in road and rail engineering.

Given Data / Assumptions:

• Simple circular curve between two tangents.
• Standard U.S./international notation: PC = start of curve, PT = end of curve, PI = intersection of tangents.
• Mid-point of the arc is not a standard control point name.

Concept / Approach:
The Point of Curve (PC) is where the back tangent ends and the circular arc begins. At the far end, the curve terminates at the Point of Tangency (PT), where the forward tangent begins. The PI is where the two tangents meet if extended. Correct identification avoids stakeout mistakes and ensures correct application of tangent lengths and offsets.

Step-by-Step Solution:

Verification / Alternative check:
Stakeout formulae use tangent length from PI to PC/PT; field notes and textbooks confirm these definitions universally.

Why Other Options Are Wrong:

• Point of tangency: That is PT, not PC.
• Point of intersection: Different point (PI).
• Mid-point of curve: No standard control name in basic curve geometry.

Common Pitfalls:
Mixing PC and PT; remember PC = beginning, PT = end of the arc.

Final Answer:
Point of commencement (beginning of curve)