The distance between the running faces of the stock rail and gauge face of tongue rail measured at the heel of the switch is known as -

Question

Prepp Team · Accepted Answer

Understanding Heel Divergence in Railway Switches

In railway tracks, a switch is a crucial component that allows trains to move from one track to another. It consists of several parts, including stock rails and tongue rails. The question asks about a specific distance measured at the 'heel of the switch'.

What is the Heel of the Switch?

The heel of the switch is the point where the movable tongue rail is attached to the lead rails or crossing assembly. It's the fixed end of the tongue rail, unlike the 'toe' which is the movable pointed end.

Defining the Measurement

The question describes the distance between two specific surfaces at the heel of the switch:

The running face of the stock rail. This is the side of the main rail that the train wheels run against.
The gauge face of the tongue rail. This is the side of the movable tongue rail that defines the gauge line and guides the wheel flange.

The distance between these two faces, measured at the heel, is a specific technical term in railway engineering.

Analyzing the Options

Let's look at the provided options and their definitions:

Flangeway clearance: This is the gap provided between the running rail and the check rail (or wing rail in a crossing) to accommodate the wheel flange as it passes through a crossing or curve. This is not measured at the heel of the switch between the stock and tongue rail.
Heel divergence: This is defined precisely as the distance between the gauge line of the tongue rail and the running face of the stock rail at the heel of the switch. This measurement is critical for ensuring proper transition and preventing derailment.
Throw of switch: This refers to the lateral distance the toe of the tongue rail moves from its position against the stock rail of one track to its position against the stock rail of the other track. It's about the movement range, not the distance at the heel.
Flare: This term is sometimes used to describe a widening of the gauge, for instance, in the flangeway of a crossing or on sharp curves, to ease the passage of wheel flanges. It doesn't specifically describe the distance at the switch heel.

Based on the definitions, the distance described in the question matches the definition of heel divergence.

Here is a summary of the terms:

Term	Definition	Measured At
Heel divergence	Distance between running face of stock rail and gauge face of tongue rail	Heel of the switch
Flangeway clearance	Gap for wheel flange passage	Between running rail and check/wing rail (e.g., near crossings)
Throw of switch	Lateral movement distance of tongue rail toe	Toe of the switch
Flare	Widening of gauge/flangeway	Various points (e.g., crossings, sharp curves)

Therefore, the distance between the running faces of the stock rail and gauge face of tongue rail measured at the heel of the switch is known as Heel divergence.

Revision Table: Railway Switch Terminology

Term	Key Concept
Stock Rail	Fixed rail against which the tongue rail rests.
Tongue Rail	Movable pointed rail that directs the train.
Heel of Switch	Fixed end of the tongue rail.
Toe of Switch	Movable pointed end of the tongue rail.
Heel Divergence	Distance at the heel between stock rail running face and tongue rail gauge face.

Additional Information on Railway Track Geometry

Understanding the precise geometry of railway track components is vital for safe and efficient train operations. Heel divergence is one such critical dimension that is carefully controlled during manufacturing and installation. Improper heel divergence can lead to issues like:

Increased wear on wheels and rails.
Rough riding.
Increased risk of derailment, especially at higher speeds.

Other important track geometry parameters include gauge ($\text{G}$), super-elevation or cant ($\text{C}$), curve radius ($\text{R}$), and various clearances and distances within switches and crossings.