As we’ve noted before, length, max weight and axle loading fluctuated drastically back in the day, although there are still variations today. Michigan was generous with overall length and total weight, but had restrictive axle loading. The result was the “Michigan Train”, a semi trailer and straight trailer combination with more axles than usual. This rig’s max. weight is 76,000 lbs, quite high for 1956. Powering it was the DD 6-71, with some 230 hp.
Here’s a somewhat newer version of Michigan trains, with GMC Crackerboxes hauling the loads.