I've tried a lot, but I can't fix this erratic data anymore.
So, I will write useful information when editing.
It may be difficult to read because the standard language is not English, but this may be useful for something.

I used google translate to make the text

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Operable train
3 trains in front of the spawn.
Consists of "train [vehicle]" directly under "main.xml [scene]" and "unnamed [group]" under it.

What is important is the density of the vehicle and wheels.
If you reduce the density, the vehicle will run at high speed, but more derailment and damage will occur.
The default is extremely high value.
Balance density and speed without derailment.

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Switch powered train
5 trains in the back from the spawn.
consists of "train [script]" directly under "main.xml [scene]".
It is powered by the "test.lua" script.

This also controls speed and stability by density.
"prop0 density" of "train_1_grp [group]" changes the density of vox in the group of the car body at once.
The density of "bogies [group]" changes the density of wheels, and the density of vox in instance changes the density of bogies.
Power is on the first wheels, the other wheels are unpowered.

The wheels rotate to move forward. The higher the density of the wheels, the stronger the movement, but that alone will cause a rampage. If the density is low, the wheels will spin freely and you will not be able to move forward.
By increasing the density of the wheels and the density of bogies, you can hold down the rampaging wheels to the track.
It is necessary to find a numerical value of density that can support the density of the car body, move forward firmly, and do not go wild.
Since the car body is subdivided, the density value can also cause natural damage to the car body.

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There is no problem with breaking it, but I have not been able to run the train normally.
I want you to edit it so that you can run the train firmly.

Enjoy modding!