Ummm.....I think actually when an Aussie talks about a "road train" he (or she) is referring to just one truck. These are (hope I am using the next word right) articulated transports with more than one trailer. They can be up to 55' long and are a common sight in the Outback. In fact there are road signs about road trains all over the Outback - because road trains are such beasts to pass on a single-carriageway highway.

I even saw a sign that said, "Warning: Road trains on roundabout" in Alice Springs. Eek!

But as far as I know, the term "road train" refers to a single vehicle, not a convoy.