As much as hate to admit it, that style of trailer was invented in euorpe (one of the few things they learned to do right, having spent several years over there working i can tell you that is one of the only things they learned) The neat part about those trailers is that each set of 2 duals steers. and each set of 2 duals has a very large hydralic cyclinder to raise and lower the trailer. it allows us to back the trailer under a load and raise it to haul hight. The trailers are like an erector set and can be added to and subtracted from to suit any load weight or size. The largest i have ever operated was 42' wide and 220' long the load we hauled weighed 3650 ton (which at that time was the largest load ever hauled by a tractor trailer combination) and it was lifted to haul height by the single 31 HP Duetz diesel that runs the hydralics (hydralics are truley amazing). We had 2 Hendrikson DPM360 Primemovers pulling it (truck weight 360,000# +200,000 counter weight, power VT1710 twin turbo Cummins (750HP and god only knows how much torque) some of the smaller loads (the one pictured) are hauled over the road, that load went through downtown Willsonville, OR at 04:30. we pulled it with the SX45 Mack w/16V71 Detroit, woke about 40,000 sleeping people, it was cool. If I have time next week I will scan some pic's of other big loads and upload them for all to see.