A friend who has been on the train may have noticed that the sleepers under the rails are one after the other, like fish bones.

But at the turnouts of the railway-that is where trains change and diverge - you see some very long sleepers that are much longer than usual.

Many are curious: How long? Why is it so long?

Sleepers used on the main line of ordinary railway are generally about 2.5 m. In the turnout area, the sleeper length increases from 2.6m to 5.5m or longer. It's not the manufacturers who are lazy, but the turnouts, which really need so long wood.

The reason is simple - the structure of a switch is much more complicated than that of a common line.

On the ordinary track, two rails are laid in parallel. Trains come and go directly on the track, with single stress direction. But turnouts are different, they are the key to dividing one track into two. When the train passes by, the wheels may go left or right, and the impact force will act on several rails and the support under them from different directions.

Ordinary lengths of sleepers are not sufficient at all - they do not support the full width of the switch structure. When lengthened, all rails can be fixed on the same foundation without running separately.

The carrying force of turnout sleepers is also greater than that of common sleepers. Trains on ordinary lines are basically moving forward, and sleepers mainly bear vertical pressure. However, when changing lanes, the wheel will produce a lateral thrust on the rail. If the sleepers are not long enough and fixed firmly enough, the rails will be pushed and moved, which will affect the stability of the driving, and even cause problems.

There is one more detail that you may not notice - the sleeper spacing in the switch area is not uniform. Spacing is similar on ordinary lines. However, the turnout area is different, with dense key stress points and sparse non-critical areas. As a result, the length of turnout sleepers changes accordingly, short ones and long ones form a complete supporting surface.

Anti-corrosion sleepers are also used, and the requirements for turnout sleepers are higher. Oil immersion depth, wood material selection and end surface treatment shall be more strict. Qualified oil-immersed sleepers for turnouts shall have a depth of at least 13mm and be black inside and outside after cutting. Or it will be abandoned in a few years under severe environment.

You may also notice that the end faces of turnout sleepers are usually bundled with wire. This is not a decoration, but a crack prevention measure. Because of its length and thickness, wood is susceptible to cracking from the ends during drying and use. Once cracked, the bearing capacity decreases directly. Wires tie the ends, which is equivalent to wearing a "tight suit" on the wood.

There are turnout sleepers in the mine and on bridges, not just railways. The tracks in the mining area are often changed to transfer ores, and the special stress of the bridge structure shall be considered for the turnouts on the bridge. Wherever, core logic is the same – with longer pieces of wood holding more complex structures.