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Possible levels for getting this achievement are: [3-5,6], [4-3,4,5,6], [5-3,4,5,6], cause they spawn 8 different train stations. I myself got this achievement on level 3-6.

The safest way to do this is with the final train of the level, so that other trains won't get in the way and create an accident as you go from one station to another. Once your tracks are clear, start the train and send it to every station once (including its spawn station) and finally to its destination.