I have seen the 16 wheel grouping lowboys here a number of times but am not aware of whether or not there are allowances for extra weight per axle. Idaho uses a bridge formula table for legal weights (allowable weight per axle relative to spacing from one axle to another), but I have not noticed any table that addresses the 16 tire groups. My annual oversize/overweight permit for Idaho as well as Montana is based upon my actual axle spacings, and shows the allowed weight for the various highways. Many of our highways do not allow as much weight as the interstate , and these are specified in the permit by a map that has the highways color coded according to the allowable weight for each.
I have seen a number of 16 tire set ups through here hauling 631's and 37's etc., so I am sure it is permitable, but I do not think that there is any additional allowance without a permit. Anything over 80,000 pounds, regardless the number of axles, has to have either an excess weight permit if the load is reduceable, or an overweight permit if it is not.
A call to our transportation department will clear it up for you. They are typically very nice to deal with. If you need the phone number let me know.
Montana's folks are nice as well, but the waiting time on the phone to someone in Helena can by excruciating depending on how busy they are. Montana also has an on-line self permitting process, but you must be registered in it and it is less than user friendly in my experience. For permits in Montana it is often quicker to call one of the Port of Entrys, as they can issue standard overweight permits as well.
Let me know if I can help!
