A thread on trains in Satyajit Ray's Apu Trilogy (in chronological order) :
In films of such small,intimate corners of life, trains acquire an almost magical role due to their symbolic weight. In Pather Panchali it becomes a rare sight of a civilisation far away from their lives
In 'Aparajito', a train becomes a symbol of the vagrant way of life for Apu and his mother in search of settlement after the death of their father. That transition from Apu's mother's face to the moving train with a swipe of the camera tells that story the best.
And later in 'Aparajito', the train symbolises Apu's departure not just from his home but from the companionship of his mother, as seen in that dissolve transition from her body to the train in which Apu is moving to Calcutta
This is one of my favorites. Apu's mother lies in a debilitated state of body and mind when a whistle from the train and a distant sight of it offers a muted sense of hope of his return. Ofcourse he doesn't, and this final disappointment leads us into her last night in the film.
In Apur Sansar it becomes a lived visual symbol of what fate would make to be a last meeting between the lovers - Apu and Aparna (Sharmila Tagore) try their best to hold on to each other, but the train drives on and takes her away, riding into darkness, leaving him behind.
Apu later returns to a similar place where he last met his wife, this time to kill himself - near a train. He isn't able to do it, and in a beautiful shot, as the train rides away in the background, all that is left is an empty sky with a curl of black smoke.