Turnout geometry: The overall length of a turnout is measured from the end of the stock rail up to which reference point in the crossing?

Introduction / Context:
A turnout diverts trains from the main line to a diverging route using a switch (stock and tongue rails) and a crossing (frog). Understanding standard measurement points is essential for layout planning, material ordering, and site setting out.

Given Data / Assumptions:

• Overall turnout length definition is sought.
• Reference features include stock rail end, toe of switch, throat, actual nose, and heel of crossing.

Concept / Approach:
Railway practice defines the overall length of a turnout from the end of stock rail (at the switch end) to the heel of crossing—the point where the wing and crossing rails effectively complete the diverging geometry before the straight lead away.

Step-by-Step Solution:
Identify starting reference: end of stock rail at the switch.Identify terminal reference: heel of the crossing, not the actual nose.Hence, overall length = distance between these two points.

Verification / Alternative check:
Standard turnout drawings and tables list overall lengths tabulated to the heel, matching site measurement practice for ballastless and ballasted tracks alike.

Why Other Options Are Wrong:
Actual nose/throat: Intermediate points used for checking geometry; not the terminal for overall length definition.Toe of crossing: Not the standard endpoint for total turnout length.

Common Pitfalls:

• Confusing nose of crossing (critical for wheel guidance) with heel position used in length definitions.
• Using switch toe-to-nose dimension instead of full turnout length.

Final Answer:
Heel of crossing