Rail will always be better than road transport but rail in Australia has a couple of big problems, unions and bureaucrats. You have to get rid of both of these obstacles before you can get efficient and profitable rail use.
Our roads are inadequate for the traffic that they already carry and the problems will get worse as time goes on.
Doubles and triples should not be on our highways as they are unable stop, dodge, or otherwise evade the normal traffic that use our roads. They are basically unsafe and although I have never seen any statistics, I fail to see how a loaded double let alone a triple can stop in the required distance
