Apparently several years ago there was a flaw in the construction methods being used, causing this issue to appear on all interstates constructed during that period. Parts of 94 are bad, 41 near Appleton is terrible, I'm sure there are others. These roads aren't so much worn out (though others certainly are!), but rather fundamentally flawed yet too expensive to rip out and replace.
In my experience, the effect varies drastically with different trailers and tow vehicles, though not necessarily by weight or length. Probably a resonance thing.
It's not noticeable in an average passenger vehicle, so there isn't much of a push by citizens to correct the problem.
