Road Trains are something that are only found in Australia. Super high horsepower trucks pulling 3 or more semi trailers behind them. These trucks with trailers can get to lengths of 50+ meters long. That's like 200 Feet! And weights ... upwards of 200 TONS! You sure wouldn't want to get in the way of one of these big monsters.
Most of these trucks run in Western Australia and into the Northern Territories in areas called the outback. Out here these trucks rule as there is not much personal traffic. You wouldn't want these transports running down a freeway that was crowded with 4 wheelers.
Running trucks like these pulling the loads they do puts extreme pressure on them. Most transport trucks wouldn't take the abuse that these trucks do. High temperatures and extreme dust make for oversized radiators and snorkel type air intakes. Large horse power and lot of gears not to mention very heavy rear ends.
Although a lot of these trucks that pull trains are tandem axle units, there are a lot of tri drive trucks. Makers of transport trucks like Kenworth and Western Star build tri axle drive units to pull these super heavy loads. Other European builders such as Volvo also build tri drive units.
Most of these train units haul bulk commodities such as grain, livestock, logs and ore from some of the mines that are in this area. Others carry fuel and some are even reefers for produce and perishables.