Here the limit on main roads is 53 metres, and there's only set routes they're allowed to use in the major cities. Out on mine sites seven trailers is common, until they get to a major roadway, then they're broken down in to smaller loads.My dad drove rigs like that and the maximum length you could legally drive on Norwegian roads was 24 meters. So those Australian ones are crazy long from my point of view.
[Edit] I forgot to mention, most of Australia is fairly flat, that makes a difference too.