Switch rail form for modern track: Which type of switch rail is generally adopted on contemporary mainline track to improve alignment and riding quality through turnouts?

Introduction / Context:
Modern turnouts aim to provide higher permissible speeds and smoother guidance into the diverging route. The planform of the switch rail—straight versus curved—affects entry alignment and impact forces at the switch toe.

Given Data / Assumptions:

• Mainline or high-class track turnouts.
• Objective: improved ride and lower maintenance.
• Compatible crossing and lead design.

Concept / Approach:
Curved switches provide a gradual change in curvature, aligning better with turnout geometry and reducing sudden steering demand on wheelsets. This yields smoother transitions, less battering, and improved service life compared to straight switches in the same lead length.

Step-by-Step Solution:
1) Identify governing objective: smoother diverging entry.2) Compare planforms: straight vs curved switch.3) Curved switch offers progressive curvature → reduced impact and wear.

Verification / Alternative check:
Track design guides and field experience show higher diverging speeds and reduced maintenance with curved switches for equivalent sizes (e.g., 1 in 12, 1 in 16).

Why Other Options Are Wrong:

• Straight switch: sharper entry, higher impacts.
• Loose-heel/bent/stub: outdated or special-purpose forms not typical for modern main lines.

Common Pitfalls:

• Confusing undercut vs curved—undercut is a planing detail, curved is a geometric planform.

Final Answer:
Curved switch.