I have never seen a bus being scaled, although we like the rest of you, have those one or two little towns close by that have figured out an additional revenue source by having a weight patrol and while traveling you may encounter one by accident, lost, complete with Barny Fife.
I think the cop would have to be a real jerk to fine a motor home/bus for overweight but if he was and if he did, in Illinois it would be 75 bucks for every thousand pounds over the limit.
So on a 5 ton limit, like the street I live on, I'd be 16 ton over w/o the toad, at 75 a thousand, that would be a 2400 dollar fine.
As far as bridges I would not cross one that was marked anything under 20 ton because of both safety and a potential fine.
There is a law for commercial vehicles that legally allows them 5 miles off any exit ramp from any interstate system for 5 reasons no matter what the local restrictions.
To sleep
To eat
To fuel
To load or unload
To make repairs
When pulled over and approached you had better be using one of these reasons cause, I'm lost or I'm going around a back-up will earn you a trip to the scale and then the cash station.