I live in Colombia, and in the town where I live, most of the adults and old people often like to start talking to the person who is sitting next to them, and have a nice conversation on the bus trip. However, I think it depends on every person. My mother often likes to talk to the person who is sitting next to her on the bus, and it's normal for her. I don't think that I'd do it sometime since I'm not get used to doing it. If someone start talking to me on a bus, I'd not feel uncomfortable, it's not a problem, but perhaps I won't carry on a real conversation.

I think it depends where.I think people in smaller places like villages chat to each other, but in big cities people are less likely to talk to you.Either they are rushing somewhere and they are too busy and in a hurry, or they are less trusting of strangers than in small places.

I grew up in Nepal. In Nepal it won't be considered totally strange to start up a conversation with a person sitting next to you. However, later I moved to the Netherlands and Canada. In these countries, I have seen that people normally don't want to be disturbed. I think it is normal for somebody to talk to person sitting next to you. If somebody isn't interested s/he can simply say so. :)

In the USA it really depends. The cultures can change greatly between places. Here in the Washington DC area it would be seen as very unusual, but the DC area is known, unfortunately, for being a place where people are somewhat cold and distant. In other cities it is completely the opposite. I sometimes startles me when I am visiting another place and I realize that a stranger has been trying to start a conversation with me.

In France, people don't really start a conversation but it's happen and personnally I like it, it's adding happiness during my day. As Ruthi said, it depends of the cities but I think it also depends of the people, their humor, and the weather! (They are happier when it's sunny). I live in a swall village but if I don't know the people I'll see, I won't speak to them (except if they start).