The Critical Connection: Fishplates (Rail Joints) Explained

What is a Fishplate?

A Fishplate (also known as a Joint Bar or Splice Bar) is a metal plate used to join two rail sections together end-to-end. Typically used in pairs—one on the inside and one on the outside of the rail web—they are bolted through holes drilled in the rail ends to maintain continuity.

While modern main lines largely prefer Continuous Welded Rail (CWR) to create a seamless track, fishplates remain essential in specific areas, such as sharp curves, switch points, and temporary repairs.

The Vital Role of Insulated Rail Joints (IRJ)

Not all fishplates are made of simple steel. In modern signaling systems, Insulated Rail Joints (IRJs) are critical components. These specialized fishplates contain distinct insulation materials to electrically separate two sections of track.

• Track Circuits: IRJs stop the electrical current from flowing to the next section, allowing the signaling system to detect exactly which “block” a train occupies.
• Failure Risks: If the insulation fails (bridging), it causes a “Track Circuit Failure,” turning signals red as a safety precaution.

Challenges with Fishplated Tracks

The “clickety-clack” sound of old trains was caused by wheels passing over these joints. While nostalgic, these gaps present significant engineering challenges:

• Structural Weakness: The bolt holes drilled into the rail web create stress concentration points, often leading to “star cracks” and rail breaks.
• Maintenance Intensity: Bolts vibrate loose and require regular tightening.
• Wheel Batter: The impact of wheels hitting the joint gap damages both the rail ends and the rolling stock.

Comparison: Fishplated Joint vs. Welded Joint

Why has the industry moved away from fishplates for high-speed travel?