Points, Crossings & Turnouts

The purpose

A railway vehicle cannot steer itself; to move a train from one track to another the track itself has to be arranged to guide it. Points and crossings (together called a turnout or switch) let a train pass from one line to another — into a siding, a loop line, a platform line or a diverging route — while keeping the main line continuous.

Parts of a turnout

Points (switches)

• Stock rails — the two continuous outer rails of the running line, against which the switch rails rest.
• Switch rails (tongue rails) — two movable rails, each tapered (the toe) at its free end to fit closely against the stock rail, and the other end (the heel) attached to the lead rails. One switch rail rests against its stock rail while the other is drawn away; the train follows the closed switch rail.
• Toe — the thin, pointed end of the switch rail that is moved.
• Heel — the end near the crossing where the switch rail is connected to the track (either hinged — a split switch — or fixed).
• Throw of switch — the distance through which the toe of the switch rail moves to open or close the points (about 95–115 mm on Indian Railways, depending on the type; check the standard plan).
• Heel divergence — the distance between the gauge faces of the stock rail and the switch rail at the heel.
• Tie rod / stretcher bars — connect the two switch rails so that they move together.
• Point machine or lever — moves the switch rails; locks hold them in position.

Types of switches: stub switch (obsolete: the entire rail ends move), and the split switch — the standard; it can be straight or curved, and thick-web (heel block) or spring types. Curved switches are used on turnouts for higher speed.

Crossing

A crossing is the arrangement where the two rails cross each other on a turnout so that the wheel can pass across.

• V (acute-angle) crossing — the crossing where the left-hand rail of one track meets the right-hand rail of the diverging track at an acute angle. Its parts: the nose (point of the crossing), wing rails (which guide the wheel across the gap), and the splice.
• Obtuse crossing (diamond, or "K" crossing) — where the two tracks cross at a wider angle (at the ends of a diamond).
• Gap at the nose — a gap must exist between the wing rails and the nose for the flanges to pass; the wheel is carried across by the tread, and the flange is guided by the check rail opposite to prevent it from striking the nose.

Check rails

A check rail is a rail laid parallel to the running rail opposite the crossing nose, at a short distance (flangeway clearance) from it, to guide the wheel flange and prevent the wheel from striking the nose or taking the wrong route. Check rails are also used on sharp curves, on bridges and at level crossings to guide wheels and reduce derailment risk.

Swing-nose crossings

In a swing nose (movable) crossing the nose of the crossing is a movable part, closed against the wing rail by the point machine at the same time as the switches, giving a continuous rail and no gap. It is used on high-speed turnouts and improves ride and safety.

Crossing number and angle of crossing

The crossing angle $\alpha$ is the angle between the two gauge faces of the crossing. It is expressed by the crossing number (or number of crossing) $N$:

For example, a 1 in 12 crossing has $N=12$, so $\tan \alpha =1/12$ and $\alpha =4.76°$. The larger $N$ is, the flatter the turnout and the higher the speed allowed on the diverging line.

The speed permitted on the diverging line rises with the crossing number — of the order of 10–15 km/h for a 1 in 8½ turnout, about 30 km/h or more for 1 in 12, and higher again for the flatter ones; the current standard plans give the exact values.