Always under the impression that all combination vehicles (other than obvious RV-only, not toters) had to stop unless ramp was full.  The signs in TN, KY and IN all say it, I would assume it's the same on the interstate system, period.  Up to them if they go after a vehicle who bypasses I guess, which if manning levels are to where I believe they are, probably 1 in a hundred actually get stopped.  (1, there would have to be a DOT officer or trooper at the scalehouse or within a mile or so to perform the stop and 2. Someone would have to look up from their phone to actually see someone go by.  Years ago, in KY (before dedicated  "vehicle enforcement" or "DOT" officers were a thing), I believe troopers were assigned to each scalehouse, and did the weighing and inspections.  Now I believe it's state employees that work the scales and inspections and it's hit or miss if there's even an officer around the place.