Whenever the issue of speed limits arises, someone will always bring up the Autobahnen. It's not really a valid argument of several reasons.
One is that the United States is a much, much larger country. It isn't economically feasible to expect that the huge swaths of interstates the US must maintain could be kept in the proper repair for high speed driving. German "interstate" highways are VERY carefully maintained to a high level and were built to exacting standards and thick roadbed to begin with. There may be a few sections of the original 1930's still in use around Berlin, not sure on that.
Second, all cars and trucks must take and pass a yearly safety inspection that is, as one might imagine, VERY thorough and meticulous. Europeans have a reputation for precision and thoroughness in this sort of thing. Equipment wise, I found the brakes and tires to be superior - coming to a "panic stop" at 150 mph will make one appreciate the safety standards they enforce.
Finally, prospective motorists must take and pass a rigorous and expensive drivers training program Fahrschule -($1500 to $2000) which includes city driving, autobahn, night driving, etc. There is a decided responsibility placed on motorists to not impede the flow of traffic as well as not doing anything unsafe. Drivers are fined for running out of fuel - stalled cars on the sides of roadways are a definite hazard.
Basically our roads, cars, and drivers are in no shape at all for high speed driving.
"Second, all cars and trucks must take and pass a yearly safety inspection that is, as one might imagine, VERY thorough and meticulous."
We have a yearly safety inspection in Virginia. I think that's why U-Haul keeps their trucks registered in other states.