I've seen a lot that are open, but I see more that are closed than open. We drive a lot, since we have a pop-up and our families live in Texas and Michigan, so I probably spend more time on the highway than a lot of people.
There are some highway patrol cars that carry very expensive truck scales in their cars. They can weigh trucks by having them drive one wheel on the scales. I don't know how they know who they should pull over, but I've seen them using those scales quite a bit around here.