As I understand it there are distinct differences between the construction of the Autobahn and your average US highway, here are 2:
1) thickness of concrete under pavement for the:
• Autobahn = 18"
• US highway 4"
(reference, The Discovery Channel show "Modern Marvels")
2) maintenance
• Autobahn, a quarter sized divit rates immediate repair
• a kettle sized pot hole may or may not face timely repair
While I was stationed in Japan, I was required to posses a professional International driver's license...bottom line, if something went wrong, it would be my fault.
I drove on the Japanese equivalent of the Autobahn, which is named the Tomie in Japan. A driver could drive as fast as they wanted but if something went wrong, the driver would be held ABSOLUTELY accountable; the standards and liabilities in Japan are nothing like in the USA. A road that is built specify for high speed use FEELS remarkable better under the car.
Out in town in Japan, on a 2 way road just wider than a full size US pick up, going 40 kph was a risk; on their standard highway with a posted 85 kph, 135 kph felt reasonable if no one else were on it.
I had an automobile that I rebuilt capable of driving over 130 mph but with any degree of prudence, more like 85-95. At 90 mph, it pulled to the ground and handled very well but the faster an automobile moves the faster things can go to crap.
That being said, though sometimes a bit of a pill to swallow, I am comfortable moving about 60 mph in a vehicle that I gave purpose build with safety as the for front; knowing full and well that the kid passing my may have less regard for their own safety, let alone mine.
Driving in arenas like Orange County, San Diego and LA California with 16/18 and 20 lane section of highway parallel to Fast pass toll lanes fir those that must get there faster, legally...I am still comfortable @ 60 mph, hopefully, with my vehicles powerplant sipping as little fuel as necessary to get the job done