The claim was that 50mph should be the highest limit anywhere, including freeways.

Combined with a hard 50mph limit imposed on vehicles. You buy a new car, it can't go faster than 50mph, period.

The movement has roots in Ralph Nader going back to the 50s https://nader.org/1970/12/11/the-american-automobile-designe...

That's a little bit out there if taken out of context. On my street the limit is 15 KM/h, on most city roads it's 30 (again, KM/h, not MPH), but on the actual highways where only cars are present and where you don't necessarily need to be, the limit is over a 100.

Now I can probably understand how one can take such radical position, when living in a place that doesn't restrict cars as much as they are restricted here. It's like being so much disillusioned with US that USSR propaganda starts to be appealing and belieaveble. I guess?