Social Etiquette

Today I was taking the bus home from school. I sit down and notice that I'm facing someone a girl who I had a class with last term. I don't really know her outside of class but we shared a couple conversations before. Even now I can't seem to recall her name.

In all honesty, I didn't really want to talk to her, but I felt obligated to say "hi" because I didn't want to act like we never met. This was all on the assumption that she had also noticed me. I never really know what to do in these situations. If she's anything like me, all she wants to do is sit quietly on the bus and be left alone...but she's not me...

After a couple minutes, I pretended that I only noticed her at that moment and said hello. We talked for a couple minutes, but I didn't know whether I should have went back to reading. She was also reading prior to my interruption and I didn't want her to feel obligated to talk to me. We ended up talking till her stop (which luckily was not very long).

I hate situations like this. If it was a good friend, I would have no problems talking to them, but for passing acquaintances it's more difficult to judge. Does the other person even want to talk or do they just feel the same obligation to make chit-chat?

Man, I sound really neurotic right now.