Anecdote from my country, where people ride trains all the time, fitting your description, although it takes a weird kind of extra ‘excuse’ in this case all the time: It would often feel weird to randomly talk to your seat neighbor, but ANY slightest excuse (sudden bump in the ride; info speaker malfunction; grumpy ticket collector; one weird word from a random person in the wagon, … any smallest thing) will an extremely frequently make the silent start conversation, and then easily for hours if the ride lasts that long.
This tracks. In Boston in the 90s, talking to randomly selected people was almost always perfectly fine. But responding to people who spontaneously initiated conversations in public places resulted in talking to some deeply weird people.
This tracks. In Boston in the 90s, talking to randomly selected people was almost always perfectly fine. But responding to people who spontaneously initiated conversations in public places resulted in talking to some deeply weird people.