Points and crossings

Points and crossings, together called a turnout, let a train move from one track to another. A turnout has three main parts. The switches are a pair of tapered, movable tongue rails that are set against one stock rail or the other to guide the wheels onto the chosen route. The lead rails curve the diverging route away from the main line. The crossing, or frog, is the point where the inner rails of the two routes cross, with a gap that the wheel flanges pass through.

At the crossing, the wheel briefly loses support from one rail, so check rails on the opposite side hold the wheelset in line and stop the flange from hitting the nose. Crossings are made of cast manganese steel or welded rails, and swing-nose crossings, which close the gap, are used on high-speed lines because they remove the impact.

Crossings are described by their number N, written as 1 in N: the ratio of the spread between the crossing legs to the length along the crossing. The larger the number, the flatter the angle and the larger the turnout radius, which allows a higher speed on the diverging route but makes the turnout longer. Common Indian turnouts are 1 in 8.5 and 1 in 12, with flatter ones for higher speed.

Turnouts are the most maintenance-intensive part of the track. Wear on switch tips and crossing noses, loose fastenings and poor ballast under the crossing must be inspected regularly. Interlocking with the signals ensures points are correctly set and locked before a train is allowed over them.