They're a prick to get stuck behind and practically impossible to overtake, although on the positive side they really only operate in the outback areas where the roads are relatively straight and visibility is good at long distances.
Maximum legal road train is 53.5m (176ft) and can go up to around 200 tonnes. They can travel at 100KM/h (62mph) so you can imagine coming around a corner to a 200 tonne monster coming towards you at speed taking up 2/3 of the road full of 4 trailers of highly flammable fuel..
On February 18, 2006, an Australian built Mack truck with 112 semi-trailers, 1,300 t (1,279 long tons; 1,433 short tons) and 1,474.3 metres (4,836 ft 11 in) long, pulled the load 100 metres (328 feet) to recapture the record for the longest road train (multiple loaded trailers) ever pulled with a single prime mover. It was on the main road of Clifton, Queensland, that 70-year-old John Atkinson claimed a new record, pulled by a tri-drive Mack Titan.
Wikipedia has a wealth of pretty useless information
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