It’s worth adding that none of the tramway or street running currently planned involves trams running in “mixed traffic” i.e. sharing with cars and lorries. The Callaghan Square section is currently planned to be a segregated section with two crossings where tram-trains will cross the main traffic lanes at traffic lights.
But I'm sure they still require the ability to run under line of sight rules in order to have those crossings. And also (unless plans have changed since I last looked) line of sight rules will also apply between Queen Street and the Bay (I don't know why).