One of the things that comes up occasionally is how some of these problems are basically due to the several states having different laws. (I think a lot of it, maybe almost all of it, is due to roadside interpretation differences, myself.) Sometimes it seems like a national ruleset would clear up some of the issues, but as far as I can tell, we *LOSE* when the federal government takes something from the states like that.
I have noticed that in more than one state, the state big truck laws are often just references to the FMCSR. The state statutes or administrative code (or both) say something like "The Department incorporates by reference 49 CFR 40, 379, 382, 383, 390, 391, 392, 393, 395, 396, 397, and 399..." and sometimes amend it to change various things, like the definition of "commercial vehicle" or what not. All of the commercial tickets that I have seen show violation of states' statutes or admin codes, not the FMCSR.
The whole thing is WAY too complex, but that seems to be pretty par for law in general.