I was told this story by an American couple I met in Prague. It's an anecdote I would very much like to believe; and I can only hope they weren't talking about themselves.
An American lady in London asked, "At road crossings, when the little green man comes up, why is there a bleep-bleep-bleep noise?"
"That's to help blind people", she was told.
"Ah!" she replied, "But in America, we don't let blind people drive!"