Rope: if your truck crosses the 26k CDL limit, or you tow a 10k trailer, you must follow all the Federal DOT regulations. NO EXCEPTIONS! It is curious, however, that some states do not attempt to enforce the regulations as rigorously as others.
Back when the federal speed limit was set at 55mph, I had a Texas state trooper drive down the shoulder of a state highway at 55mph for about 5 miles...until I finally passed him, and went speeding down the highway at 65mph! After I passed him, he pulled back onto the highway and faded into the distance.
Many years ago, when I was driving "over the road", each state had it's own regulations, and they were often quite different.
Missouri, Arkansas, and Illinois each had legal weight maximum at 73,280, and a 55' maximum semi-truck length limit, with a "full truck" length limit at 65'. This rule was so the car-carriers could be longer. New Jersey was a 73k state too, but not too many trucks worried about them. Too small a state, and too easy to go around the scales.
Collectively, these three states choked off the east to west coast traffic, and they made zillions of $ in fines. You see, those three states form a vertical barrier across the whole middle of the US for a 80k truck loaded with California veggies headed for the New York grocery stores. All the semi-trucks were limited to small and light, the trailers were never longer than 45', and almost all trucks were "cab-over" design so that they could go down I-90,I-80, I-70, I-44, and [whatever Interstate highway Arkansas has] with a legal load.
Eventually, comes along a new President (Reagan), a new ideology in government, and Presto! De-regulation of trucking, along with some real pressure by the US gov. to make the states toe the line and bring all the DOT regulations into a standard format. So...nowadays all the states MUST follow the federal regulations, and what works in California is good in Missouri. The cab-over truck is almost completely absent from the highways, and we get State DOT audits in our offices to make sure that we aren't breaking any federal regulations.
I think Michigan still has a GVW weight limit at 132,000 pounds, and a 12 axle limt, so there are exceptions.