rail joint
A join between two rails in a railway track placed end to end; the rails are joined by fishplates where joints are not welded.
rail joint: where two track rails meet and transfer load
A rail joint is the connection point where two lengths of rail meet end to end on a railway track. At this joint, the full load of train wheels and the rail itself must transfer smoothly from one rail section to the next without creating a gap, deflection, or stress concentration that could cause derailment or fracture.
The traditional method uses fishplates, also called angle plates or splice bars: two steel plates bolted on either side of the rail web, one under the head and one under the foot. The bolt spacing and plate dimensions must match the rail profile; a 60 kg/m rail uses different fishplates than a 50 kg/m rail. Each joint typically requires four bolts per side, though some heavy-duty applications use six. The bolts are torqued to a specific value to prevent both loosening from vibration and over-tightening that could strip threads or crack the rail.
Welded joints versus bolted joints
Modern rail installation increasingly uses welded rail joints, where the two rail ends are fusion-welded together and the weld bead is ground smooth. This eliminates the discontinuity, reduces maintenance, and improves ride quality. However, welded rail requires careful temperature control during installation to avoid residual stress. Bolted joints, though noisier and requiring periodic tightening, remain common in older lines and in places where rapid repair is needed.The bolted joint creates an audible click or clack as train wheels cross it; this is the most recognizable sound of traditional railways. The impact is caused by a slight depression or wear that accumulates at the joint zone, particularly on the head of the rail where the wheel flange rides. Over time, bolt corrosion, metal fatigue from cyclic loading, and wear of the fishplate itself weaken the joint.
Failure modes include bolt shear, fishplate cracking, rail head breakage around the bolt holes, and lateral movement of one rail relative to the other. Latterly, ultrasonic inspection is used to detect internal defects and cracks in the rail near joints before they propagate. On curves and steep grades, joint wear accelerates because of increased lateral forces and slip.
The rail joint remains a weak point in track geometry; many track defects and maintenance interventions occur at or near joints. This is why continuous welded rail, which eliminates joints entirely over long distances, has become standard on mainline routes where track quality and speed are priorities.