Parallel play was invented in trains, I mean they are so nice to be on, all at once you can watch a movie while one lady reads a book, 4 drunk people discuss the nature of the universe, a boy plays a ds game, some idiot gets work finished and a 17 year kills a demon, the variety of activities in one space help to contribute to the calming atmosphere of a train, it manages to intrest and provide atmosphere without being overstimulating.

Warning: this is not a scientific claim however and is just what I feel makes trains cool