Degree of a railway curve (India): The degree of curve is defined as the central angle subtended by an arc/chord of length

Introduction / Context:
In railway geometric design (Indian practice), curvature is commonly expressed in degrees rather than by radius. The “degree of curve” links field measurements (using chords) to the underlying circular geometry.

Given Data / Assumptions:

• Indian practice uses a standard chord length of 30.5 m (100 ft).
• Degree of curve is the central angle subtended by this standard length.

Concept / Approach:
Defining the degree of curve via a fixed chord length allows easy field setting with tapes and theodolites. With a 30.5 m chord, the larger the angle, the sharper the curve (smaller radius).

Step-by-Step Solution:
Adopt the conventional standard chord = 30.5 m.Degree of curve D = central angle subtended by that chord at the circle centre.Thus the correct value is 30.5 m.

Verification / Alternative check:
Field tables relate radius R and degree D using the 30.5 m basis: R ≈ 1750 / D (approximate in metres), consistent with this definition.

Why Other Options Are Wrong:

• 10, 15, 20, or 30 m: Not the standard chord adopted in Indian railway practice.

Common Pitfalls:
Confusing highway practice (where other definitions may exist) with railway standards; mixing chord-length and arc-length definitions—Indian fieldwork uses the 30.5 m chord convention.

Final Answer:
30.5 m