I'm sure most of you would agree that people tend to keep themselves on BART and those who reach out to strangers to strike up a conversation are perceived as weird or annoying 95% of the time. People who are not reading a magazine, listening to music, or engrossed in their device, generally just keep their head down or their eyes closed.
To demonstrate this anti-social nature on BART, 2 friends were standing within 4 feet from each other today, looking opposite ways. It wasn't until Embarcadero, where one was getting ready to leave and finally looked up, the two realized that they were standing next to each other the whole time. They hugged briefly and chatted for 10 seconds before one had to exit.
Interesting the extent to which people keep to themselves on BART. It's so true. I usually am glued to my iPhone or a magazine (when there's no connection). I would not know who is sitting behind or across from me!