The Breathing Track: Railway Expansion Joints Explained

What is a Railway Expansion Joint?

A Railway Expansion Joint (often called a Breather Switch or Adjustment Switch) is a specialized track component that allows the rails to move longitudinally—expanding in heat and contracting in cold—without interrupting the continuity of the wheel path.

Unlike a standard gap at a fishplate, an expansion joint acts like a sliding mechanism. It consists of two tapered rails (a stock rail and a switch rail) that overlap and slide against each other. This design allows for significant movement (sometimes several hundred millimeters) while keeping the track gauge constant and providing continuous support for the train wheels.

Why Do Tracks Need to “Breathe”?

Steel expands when heated. In Continuous Welded Rail (CWR), this expansion creates massive internal stress. While heavy ballast usually holds the track in place, certain locations require physical movement to prevent disaster:

• Long Bridges & Viaducts: Steel bridges expand and contract significantly more than the earthen ground. If the track were fixed rigidly across a bridge, the difference in movement would tear the track apart or buckle the rails.
• CWR Transitions: At the ends of long welded sections where they meet jointed track, expansion joints are used to release accumulated thermal stress safely.

Structure: How It Works

An expansion joint looks very similar to a standard railway switch (turnout) but without the moving parts to change tracks.

• Scarfed Cut: The rail ends are cut diagonally (tapered).
• Overlapping: The tapered ends slide side-by-side. As the rail lengthens, the overlap increases; as it shortens, the overlap decreases.
• Wheel Path: Because the rails overlap, the wheel never hits a “gap,” ensuring a smooth ride even while the track is expanding.

Comparison: Standard Joint vs. Expansion Joint

It is important to distinguish between the small gaps in old tracks and these complex devices.