Since a while now we have these subway access gates. The main idea is that everybody would pay for their ride. Pretty soon you saw people piggy backing with people that did pay.
Not so long ago I saw a couple of 8 year olds outsmart the adults :). Instead of all, one by one, forcing themselves through the little gate only one did it. He went to the exit gate that opens without any verification. The kid let his friends in and off they were to discover the world.
I personally think it is wrong not to pay for public transport but I must say that I liked the fact that adults got outsmarted by 8 year olds.