This is also mostly true in the US but replace the backpackers with people who often have little or no reason to be on the bus at all; panhandlers or people who

This is also mostly true in the US but replace the backpackers with people who often have little or no reason to be on the bus at all; panhandlers or people whose specific motive during the day is to harass people on the bus for money or fun. There are people who spend all day on the bus following its route back-and-forth to harass passengers. It's a not-insignificant amount of people; I have no doubt they exist in some form in other countries and maybe the generalized social solution lies outside the transit system, but I do think it's a product of having truly public transit in a place where the public is a sample of everybody everywhere. EDIT: The distinction I make with a carpool is that you all know each other - you know the passengers, you know the drivers, everyone knows each other, the social contract enforces that nobody does anything too off-putting. Truly public transit has to assume that every passenger is a stranger to the other, and that's harder.