Reading Railroad
The Girl on the Train is clearly referring to Rachel, as she is the only girl who gets on a train in this book. She's also the one the reader can most closely relate to, because like us, she is an outsider looking in. She's observing and coming up with stories for the people she sees. What she doesn't expect is for her life to intersect with those she observes—after all, she's on a train running parallel to the action. She isn't supposed to get perpendicular with it.
The train serves as a metaphor for Rachel's life. She's commuting to work and back, over and over again. Except… she isn't. She's faking going to work since she lost her job, going back and forth each day for no reason. She's literally going nowhere, and it's a pattern she needs to break, just like her alcoholism. But she thinks it's her fate:
That's my train. It's the one I take. That's the way it is. (15.144)
Importantly, the train isn't even well-maintained. The reason Rachel has so much time to watch Megan and Scott is because the train stops every day. She explains, "This section of the track is ancient, decrepit, beset with signaling problems and never-ending engineering works" (1.2). This part of the trip is either another metaphor for Rachel's life or it's like traveling by rail in the United States. Either way, it stinks.
Only when Rachel gets off the train does she start to go somewhere. Talk about irony. As she says, "I am no longer just a girl on the train, going back and forth without point or purpose" (7.202). She makes up a story to get into Scott's life and help him find Megan. When she's exposed, she tells him, "You wouldn't have taken me seriously if I'd just been some girl on the train" (27.29). To us, though, Rachel is not "somegirl" on a train—she's the girl on the train.
See, the other women in the book don't get on the train. Anna doesn't like trains, and she wants to be away from them: "All those faceless bodies staring out of the windows, staring right across at us, it gave me the creeps" (20.11). As for Megan, well, though she doesn't, we're pretty sure she'd benefit from getting on a train and never coming back.
One last bit of train-related irony is in the ending… so chug on our "What's Up with the Ending" section to continue the analysis.