Railway triangle (wye) — what is the principal purpose of providing a track triangle in a yard or terminal?

Introduction / Context:
A track triangle (also called a wye) is a triangular arrangement of turnouts and connecting tracks. It is an economical alternative to a turntable for turning locomotives or entire trains, used especially where space allows but turntables are not practical or available.

Given Data / Assumptions:

• A standard three-leg wye with turnouts enabling forward movement through the triangle.
• Locomotive or rake can enter, run forward along legs, and emerge reversed (180° turned).
• Operational need: changing direction rather than simple crossovers or sidings.

Concept / Approach:

By traversing the three legs in sequence, a locomotive effectively turns around. While triangles may incidentally facilitate shunting, their principal design purpose is directional reversal. Crossovers specifically connect parallel tracks; branch divergence uses dedicated turnouts but not necessarily a full triangle.

Step-by-Step Solution:

Verification / Alternative check (if short method exists):

Operational manuals and yard schematics show triangles used primarily to reverse locomotive orientation without lifting or rotating machinery.

Why Other Options Are Wrong:

Branch line divergence uses a single turnout, not a full triangle. Crossing between parallels is a crossover. Shunting is a general yard activity, not the core reason for a triangle. Balancing axle loads is unrelated.

Common Pitfalls (misconceptions, mistakes):

Confusing triangles with crossovers; assuming triangles are mainly for general shunting rather than turning.

Final Answer:

changing direction of engines through 180°