Parts of a track

A railway track is a load-spreading system, like a road pavement, but built from discrete parts. Rails guide the wheels and carry the load. Fastenings hold the rails to the sleepers at the right gauge and inclination while allowing small movements. Sleepers, today mostly prestressed concrete, spread the load and keep the gauge. Ballast, crushed stone below and between the sleepers, distributes the load, resists sideways movement, and drains water away. Under the ballast is the formation, a prepared layer of compacted soil.

Indian Railways' main lines use broad gauge, 1 676 mm between the inner faces of the rails. Most newer metro systems and high-speed lines use standard gauge, 1 435 mm, although the earliest Delhi Metro lines were built to broad gauge.

Long welded rails remove most fishplate joints, giving a smoother, quieter ride. Their thermal expansion is restrained by ballast and fastenings, with switch expansion joints at the ends.

Ballastless track, a concrete slab with direct fastenings, is used in tunnels, on viaducts and on high-speed lines where accuracy and low maintenance matter.