IIRC the design standard for an Interstate grade highway is 75mph, not 150mph.
The lanes, ramps, etc. are designed for that speed.
that’s the difference. That’s why those higher speeds on the autobahn don’t feel much faster. I had a VW Golf and just cruised in the middle lane at 160 kph / 100 mph with much faster, better cars whizzing by me in the left lane.