b trippples and b doubbles, page-3

K & S and Toll lease and / or operate their own railway business between all capital cities alongside their road freight activities.

B Doubles do reduce the actual number of trucks on the road due to their additional capacity, as for every two B Doubles they generally have the capacity of three standard semi trailers. But, they are also restricted as to what roads they can travel on.
Interestingly, Qld Transport internally say if they had their time again they would not approve any B Double operations in Qld?

B Triples may be OK on selected routes, such as they are now, but certainly no good in the general freight task as road design could not cope. It would be totally impractical to use them on anything but minimum dual carraigeways for a start as the ability to remain at a reasonable road speed on hills as well as accelerating to rejoin traffic becoming a big issue. This would be the main cause for concern I would say as to why they didn't allow.

If you have ever manouvered a fully loaded B Double along many of the suburban routes they are allowed on you appreciate how silly it would be to allow B Triples!
Pulling up a 64 Tonne B Double in a hurry can be heart stopping stuff in itself, let alone a possible 80 Tonne B Triple!