If I was gonna do this for a living,I'd:
* lose the rig
*buy a Class-7 bob-tail turbo-diesel tractor
*and pull a 5th-wheel low-boy trailer, with the load hugging the ground, rear axles behind and above the trailer floor.
*this would reduce frontal area
*get the center of gravity down
*then construct some adaptive,multi-purpose nose fairing which could be taken down after each delivery.
*or fashion a cushioned inflatable airbag which could be strapped to the buildings nose for the trip,then unstrapped upon delivery.
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*the tractor could be optimized independent of the loads
*the loads are where the major drag is
*the buildings are around Cd 0.88
*softening their nose could get them to Cd 0.45 or so
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*technically,the tractor should be just as large as the building your pulling
*and no gap in between
Here's what NASA did to their semi-trailer
