If they’re older than 25 years old, they can be driven on the highway in the USA because they’re exempt from EPA and crash safety standards. That said, I’ve driven one 10k miles mostly highway and I would not recommend it. The car tops out at 120kmh at the redline and is very light and top heavy, so it can almost be blown over in the window.

It varies by state. Limiting them to roads with speeds <50 or so is somewhat common.

There are two sets of regulations IIRC.

If it’s older than 25 years on import, you can bypass FMVSS/EPA/DOT regulations, so they are always perfectly legal to drive on the federal highway system (incl. at 70-80mph). Some states will refuse to register them though, such as Minnesota or Oregon.

Separately, some states have an import process for cars newer than 25 years old which allows them to be licensed as UTVs/ATVs, so they can go on local roads but are usually speed limited. And iirc, they can’t drive on federal highways.

Innnteresting. I'm going to have to look into it again with that in mind. I really would like to own one.

I just drove my father-in-law's kei truck through southern Japan for about 5 hours in total, mostly on the "express". Even mild wind had me legitimately scared a few times, and it has no guts when it's necessary to pass.

Besides that it was a blast to drive, it feels more like an oversized toy than a vehicle.