Taxi Driver - Increasing Intensity Troughout the Movie

At the start of this movie, we are introduced to a normal seeming guy, getting a normal job in a normal (although quite run down) city. His job as a taxi driver starts out very standard. However, very subtle changes take place throughout the movie. It starts small, but is soon noticeable. As Travis gets more and more frustrated with the city, everything around him starts to seem crazier. Most noticeably the city becomes more and more degenerate while he talks about having to clean it up, many of the people he picks up or hangs out with become more wild and dangerous, and Travis himself as a result (or vice versa depending on how you interpret the movie) becomes more, for lack of a better term, hardcore. By the climax of the movie Travis is sporting dual pistols and an outlandish hairdo and outfit. Looking back at the beginning, we would have never expected the man then to do this. The subtle changes that happen plus Travis’ dialog to help pull the viewer along with his train of thought make the movie and Travis’ actions more believable and interesting. A fascinating addition to this process is the very end of the movie, when he picks up Betsy. Everything is incredibly similar to the beginning. The city is shown more peaceful and Travis himself has seemed to revert back to who he was before. This poses the question of reality in this story, did all of what he did actually happen? Or was it imagined, or did we perceive the world through Travis’ eyes in some way?