If you can make a 1000 km straight road somewhere in Nevada, it'll be cheaper and more efficient to do exactly that. Neither drivers nor investors would like increased travel time and costs because of the fatigue and boredom. The real improvement would be to make wider lanes and allow driving 200 mph. Or even better, put a high-speed train or a hyperloop.
60 mph is not safe on narrow streets of Paris either. Does it mean 60 mph should not be allowed where it's safe?
If you have wider lanes, more lanes, better tarmac and smooth road with safety lanes, people can drive 150 mph without a problem. Like in Germany, for instance. If the road is not safe for 150 mph, then you should drive slower.
Geez I remember my dad's Toyota Camry would start shaking at just 140 km/hr (87.5 mph.. holy crap maybe I was about to time travel). Many cars, and especially most drivers, just can't go that fast safely..
My first car (an '87 Subaru DL, which I had in 2000-2002 IIRC) started shaking between 70 and 75 MPH. My parents regarded this as a feature, because as a new driver I really had no business going faster than that. They were probably right.
