The Silent Guardian: Check Rail (Guard Rail) Explained

What is a Check Rail?

A Check Rail (also known as a Guard Rail in North America) is an additional rail segment laid parallel to the running rail, typically mounted on the inside of the track. Its purpose is not to support the weight of the train, but to guide the wheelset laterally by coming into contact with the back of the wheel flange.

While standard rails support the vertical load, check rails manage the horizontal forces. They act as a physical restrictor, ensuring that the wheels follow the correct path in critical areas where the risk of derailment is high.

Two Critical Applications

Check rails are primarily used in two specific scenarios, each serving a slightly different safety function:

• In Turnouts (Switches): This is the most common use. A check rail is placed opposite the “frog” (crossing point). It pulls the wheelset away from the frog’s nose, ensuring the flange does not strike the tip of the crossing and derail or damage the component.
• On Sharp Curves: On very tight curves, the centrifugal force pushes the wheel flange hard against the outer rail (High Rail). A check rail is installed along the inner rail (Low Rail) to hold the back of the inner wheel. This shares the lateral load and prevents the outer wheel from climbing over the rail head.

The Concept of “Check Gauge”

The effectiveness of a check rail depends on a precise measurement called the Check Gauge. This is the distance between the running edge of the frog and the acting face of the check rail. If this distance is incorrect, the check rail will fail to pull the wheel over effectively, leading to a collision with the frog nose.

Comparison: Check Rails vs. Running Rails

Although they look similar, their roles and wear patterns are different.